"Not so bad" like... he seems like a good guy. What's hard to understand?

[ Gosh, Annie. He's trying to express moderate approval here -- just in terms of people who seem decent enough to be friends with, at the very least. Light doesn't strike him as weird or, even worse, annoying. ]

Most of them just wanted something out of us. I got bothered plenty, but at least I could help out some of the other people who couldn't stand up for themselves. I talked to that Light guy again there, too, but he didn't mention you.

[ So Reiner wouldn't have known without further context there was anything "about" the two of them to know. ]