If Gabriel were someone a little less sadistic, he might feel that maybe this would constitute disproportionate retribution, especially by getting Sam involved. Still, he's twisted enough to enjoy doing this with the bare minimum of provocation, and realising that Dean had gone after his brothers as well as him just makes him even more determined to make him pay. Doubly so, since he has Raphael's support in this: having a coconspirator again is one hell of a motivator. And how seriously Dean is evidently taking this is more satisfying than it really should be.

When Dean enters the woods, Gabriel goes invisible and follows not too far behind. He'll keep away the dangerous beasties for the moment, lest they ruin his fun, but at this stage he's more concerned with keeping Dean on his toes. A snapped twig off to his right, a rustle of something dark and unreasonably big in the trees up above him... half the fun of revenge is the build up, after all.