They'd already completed the check I think. March didn't get treatment for a minute or so as the game went on, that was when the VAR check was happening. I might be wrong, but I think it was done before the game stopped for March.
The only explanation I can think of is that they are under pressure not to allow VAR to take up too much time and on first viewing, it appeared the ball came off Digne.
I must admit, I watched the game on TV, and from one angle it looked like it was just a tackle with the ball coming away off...