[Hendog]

Tough call...

I'd say if it was a narrow street and he had a large vehicle (tuck) and was not able to get into the spot in one "swoop", then it's not his.
On the other hand, he did spot it first and "claimed" it with his signal light.

Technically, he's on the wrong side of the street. Was there a double solid yellow line?

Out of courtesy I would have let him have it; or if I was driving around for a long time looking for a spot then maybe I wouldn't have, but likely would not have been the case. Each case is different.