Well it's still a drop-off from last year, unless his numbers last year are unsustainable.
How many catches in the history of the game regularly posted OPS+ over 140?
Yes, what he did was unsustainable, unless you believe Alex will go down as one of the top 3 or 5 greatest catchers of all time.
A 120 OPS+, somewhere in that range, is all that could reasonably expected of him, and he's doing that.