Because you're on Known, you're definitely sending webmentions (presuming you're using the default set up), but it may be the case that gRegorLove isn't accepting them, or it's possible that he's moderating them too (which several definitely do). [According to https://indieweb.org/webmention, he's both sending and receiving.] Not everyone in IndieWeb necessarily accepts webmentions (yet). You could ask him in the #indieweb IRC, or alternately ping him via @mention in Twitter as he often syndicates his content there as well to check.