I didn't see restart, so I can't comment on that.
I saw the lead up to ref going to monitor, then reports saying no penalty.
So I am speculating as to what happened.
The fact that he started with a dropped ball, based on what others are saying, I'm assuming the "foul" happened before offside offence meaning by overturning it, it is a dropped ball. So he went to the monitor for the foul and not offside as per what others have said (and the screen). But he could have gone to the screen for the offside to determine himself what order it was as the outcome/restart varies for each.
Foul first (given)/offside = pen
Foul first (not given)/offside = dropped ball
Offside first/foul (doesn't matter if foul or not) = IFK.
Game must restart correctly and it falls on the onfield referee to get it right.
Getting it wrong could be bad for officials their credibility and by sending official to screen for any of these scenarios is best outcome.