The pre-match favourites were leading by a goal to nil when Scott Sinclair went down in the penalty area under the attentions of Cedric Kipre.
There was minimal contact between the players but Thomson decided to point to the spot.
Moussa Dembele stepped up and coolly slotted the ball down the centre of the goal, doubling the advantage secured via James Forrest’s opener and sealing Celtic’s victory.
Robinson wasn’t only unhappy about that decision, he also feels Motherwell should have been granted a penalty of their own just a couple of minutes prior.
He said: “The game’s over as a contest when he sends Cedric off and gives the penalty.
“I’ve seen it back and in my opinion there’s no contact. The kid’s distraught, he says he’s never touched him.
“Congratulations to Celtic, they’re a super football team, but the manner we lost - it’s difficult to play against them with 11, never mind with a man sent off.
“Craig (Gordon) made a brilliant save from Louis Moult and then we had a potential penalty at 1-0 with Louis Moult as well, I’ve seen that back and it looks a blatant penalty.”