Yes, this is not an issue in OTB chess, as you won't be playing two games simultaneously unless you are a strong player doing a simul, in which case you are better than your opponents and have no reason to copy moves.
It's also not normally an issue in live chess for the same reason. It's normally only an issue in a correspondence format such as chess.com's daily chess.
And you're right, a few moves won't normally get someone banned. I've had simultaneous games that started with the same opening, simply because my opponent and I happened to want to play the same opening in both games. The games diverged later in the opening.
This is the game my banned opponent copied. Knowing I was playing a computer in the other game put me off this one quite badly. I was spending too much time on the other one. I know I play at a certain level and losing like that against a weaker player meant I was playing a computer, when you consider how difficult the moves are to find. They may seem to look obvious just looking at the game but ...
Anyway, I made a real mess of this game and my opponent played well to find the solution. I haven't analysed it yet, to work out what I should have done. I normally have no trouble with this opening say in an otb with 90 minutes each player, which is standard for UK league play. Maybe in a tournament or county game I'd play differently.
And this is the game played by the person who was banned. You can see how he copies the moves of the other player at first. This is not a normal way for white to play the position, with such an early Be3. I decided I had to deviate and the .... Nd7 move seemed a natural way to do that.
this is one reason I have a "backup" opening in case my opponent decides to play my opening against me with opposite colors. helps to know more than one opening well even in blitz games so you can spice it up every now and then.
I can't see how this helps with someone doing the hustler copycat simul trick? Regardless of your opening you end up playing yourself