You have heard correctly. MoviePass requires you to be physically present at the theater before "checking in" to the movie for which you intend to purchase a ticket. Only then can you use the MoviePass Mastercard to buy your ticket.

So you can pre-book and reserve seats, but only in person. If you live very close to a theater, you could pre-book at lunchtime and come back that evening to watch the movie, for example.

It definitely requires you to be physically present, though. There is no online ticket-buying with MoviePass.