First paper published, follow-up paper rejected by editor as out of scope? I published an article few months ago in a journal. I sent another article to the same journal, in which I improved the design idea and enhanced the computation.
I was told that my second article was sent to Prof. X (name was provided) as a topic editor. 

After about 70 days, I got an editorial rejection due to the article not being within the scope of the journal. In the online submission site, it said that my article was under review for the last 70 days.
In the end, my article was not even sent to referees... is that normal?
Yes, it is normal that articles get rejected as not in the scope of the journal. Yes, it can take a long time for the people in charge (often doing this pro bono) to get around to take a look at an article.

So you published something related before in the same journal. OK, maybe they just want "new results", not the elaboration/extra details on previous ones. Or they don't want "enhanced computation" (presumably more detailed results), and prefer description of methods. Without an awful lot of additional information, we can't tell. Besides, whatever the case may be, the powers that be at that particular journal have the last say. If we consider it normal or not, is totally irrelevant.