If Riker was trying to keep a low profile because of his support of Pressman during the Pegasus mutiny, he did a crappy job of it. He rose from ensign to commander in, what, 7 or 8 years? That's a meteoric rise that was sure to get attention. Maybe Pressman had something to so with his climb to the top, maybe just to get Riker sent off into the wilderness and far away from him. But apparently Riker just wouldn't take a ship!
mutiny was covered up until Riker came forward. It's likely that only a few people in Starfleet knew the details of what happened. Picard used up several favors just to see a preliminary report on the ship's disappearance.
If anything, Riker probably reasoned that he should do everything possible to distinguish himself in order to extinguish any doubts about his trustworthiness following the loss of the Pegasus
. Pressman may have played a role in helping Riker find another posting, but Riker still had to perform well enough to earn the promotions he received.