Here's what you could do.....

Mention to the guy, the next time you see him, "I think I saw your cat a few blocks away from here the other day. It looks like someone may be feeding her in hopes of keeping her." And see how he reacts. If he says "WHERE?" just say "it was 'so and so' street but I can't remember the exact block."

If he ends up saying "GOOD" or anything similar, that sounds like permission to me.