The conditional 2nd rounder in this deal doesn't mean anything as they are always arranged in away not to convey. So the deal really is the Celtics are sending Oklahoma City some money to take Poirier's small remaining contract off the Celtics books. If the Celtics couldn't find a deal like this, my strong guess is they would have just cut him by opening night so another player could take his roster spot.
Poirier seemed like a fun, good natured guy who fit in with the likable 2019-2020 Celtics edition, but when given playing time he wasn't effective.
Here are additional details:
Thunder will take Vincent Poirier and his $2.5 million salary into one of their traded player exceptions, according to a league source. C's include cash to cover his salary but free up a roster spot.