Is it normal for professors to twist the truth about their labs? This is related to my previous question here.

I'm enrolled in a MS/PhD integrated program in computer science at a South Korean university and have just started my first semester. In the linked question, I discuss my desire to quit my program, get my master's degree, and go for a PhD abroad.

The reason I want to quit is that when I first talked to my advisor in March, I told him that I noticed his lab does a lot of work that I'm interested in (NLP and finance). He told me that he'd be happy to have me and that there are "many research projects in those fields going on."

This is partially my fault, but when I entered the lab, I found out that the professor's main interest is bioinformatics, and that he's pretty much only involved with work relating to that. This is also where most of the lab's funding comes from. The fact that my professor's interests don't align with my own is more than enough for me to not want to do my PhD here.

Most of the students here, including myself, barely get any guidance from the advisor and usually teach themselves or learn from upperclassmen. I'm currently involved in a bio project that I don't want to be a part of. I've told some upperclassmen about my plans to go abroad after quitting my program midway, and they told me that there's a lot of people who are in the same boat. They said I just have to do the bare minimum to not get on my advisor's nerves and then I can do my own thing in the meantime. I was also advised to talk to the professor early on about my plans - despite having me told him twice before already - so that there aren't any misunderstandings in the future.

Is this normal? Do professors usually twist the truth to entice students into joining their lab?
I think your perception of twisting the truth is correct, but I wouldn't call it lying if this is your interpretation. The twisting of the truth is more produced among professors and group leaders by students that don't know exactly what topic they are interested in exactly and should pursue for PhD work. I think you are a in a minority, burning for a exact topic. At least when you don't have to pay for your PhD work, but have a salary, my impression is many PhD students choose their department/group/topic rather based on criterions like salary, infrastructure, need to move, location and culture than topical or research-related criterions. 

Group leaders need simply good people to work in their labs, and they are looking for really good people or mediocre with very much hands-on experience for a distinct project. A group doesn't act like a company with very specific job description. You need a team that is able to develop and learn, as science never stands still. Maybe your professor wants to go more into NLP and finance in future. Especially young group leaders have to dive also in new topics and broaden their scope. So this you should discuss with him. But in general his "approach" is right to make you interested in his group and not deliver you reasons on a silver tablet to not join him.

If there is too much truth twisting can and should also be proven by you. Good groups hava a good publication track and often an alumni section on their website. This is something I would always throw an eye one before talking to group leader. What research did he 5 years ago, last year, how much people work on distinct topics and has the group many collaborators and of which quality? 

The group may currently not work on your topics, but have a better infrastructure than other groups to work on it. This is something you have negotiate and outline with the professor before starting any contract, in best case by a binding research proposal, so there are no misunderstandings for what you will get your PhD and work on mostly.

That competition and working pressure is really high in south korea is not unknwon, as suicide and emigration rates of academics to have an easier life. 

I'm not sure why often professors are here on the academia.se treated as holy cows or responsible for everything. No researcher is trained to become a professor like a surgeon, it's learning by doing and they are humans like everybody else with personal inadequatnesses. They are no own species like it often sounds here. If the truth is twisted a lot, then it is rather a problem of academia at your university or country or the general culture. Of course professors are in competition to get good people, like everywhere else outside of academia.