What happens when Smeargle cannot Sketch a move?

Solution 1:

If Smeargle cannot learn the move it tries to copy, it will simply learn a random move from its available move pool. This goes for both fast and charge moves.

While snapping pictures of Registeel this morning, I was lucky enough to be photobombed. Smeargle learned Karate Chop instead of Lock-On. This has happened to other trainers as well.

Apparently (at the time of writing of the reddit thread at least) Smeargle could not learn Psystrike and learned Hydro Pump instead.

Another trainers Smeargle learned Blast Burn after photobombing a Lucario instead of learning its original charge move (my guess would be Aura Sphere, since Aura Sphere is a newer move introduced within the last year).