That hole size part is correct, but a long line seems like it would be a problem. That's why microwaves have circles instead of parallel lines. That hole size is aimed at the 2.450 GHz range.

That does beg the question about the gap around the door though. 🤔 Maybe they just figure that most of the waves won't be aligned and so the leakage would be acceptably low (e.g. not going to burn anyone)?