I emailed the professor a research idea, he responded: "Just go ahead". Is this an ok? I'm an undergraduate in CSE doing research this summer under the guidance of a professor. After an initial repeating of a previous experiment, I've been reading relevant research papers for three weeks. The program ends on August 3rd, so I have less than a month left. The professor hasn't said anything to me these past three weeks, and I don't really know what to do since this is my first time. He is rather busy.

On Friday (3 days ago), I emailed him some general ideas of a research direction (very informal, I don't think it was really a research topic proposal), and he responded: "Your ideas make lots of sense. Just go ahead". Is this an "ok"? I feel like he's upset (because of the word "just"), but I might be overthinking. Sorry kind of a stupid question, but this means I am free to continue (and that) he's not upset? 

Thank you
So, short answer, that's a yes. However, I think that he wants you to start exploring those ideas and get back to him with more content beyond of what you extract from those papers. Some proof-of-concept or similar.