He was smiling because he finally thought his tactic paid off and he got Johnson to snap and get himself ejected. I dont think he expected to be ejected as well and while I dont agree with his b**ch tactics he didnt throw a punch and probably should not have been ejected.
Clearly Innegans tactic was to act cheap and take cheap shots to try and get under Johnsons skin and apparently he has been doing this for years. So Johnson finnally caves and snaps and he is a hero. Its like when the older brother finnally snaps because his kid brother wont stop kicking his seat you understand why he did it but doesnt make it right.
IMO Finnegan maybe should have been dealt with after the game for being the instigator but he didnt throw punches so why should he have been booted. I agree with another posters question about why the ref was ignoring Innegans idiocy.