Even if he sent the files right away there would always be reason to suspect that he didn't just send you a sanitized version, but the more time that elapses the more time he would have to clean out any nefarious code.

This of course assumes he would even send the files in the first place, as sending them off to a random stranger who says "trust me I won't reveal them" is not very reassuring either. This whole topic has a sort of den of thieves feel.