Was it a push/charge in the back... two angles were tough to say. One angle sure looked like it. Was attacker waiting for the contact and kicked his legs back? I think so but there is a charge/push in the back in my opinion. I'm good with a PK.
Now for the card.... Evaluating DOGSO... Distance to goal = yep, Defenders = yep last man, Direction = yep. Straight at goal, Distance to ball = this is where I think it fails DOGSO. He is close but very questionable that he would retain possession of the ball had the push/charge not occurred. It sure looks like it will remain a 50/50 with the keeper and probably the keeper getting there first. I do not believe DOGSO is appropriate on this one. It is just not obvious.
I think the YC for SPA is the right decision.