Some eagle-eyed comics readers probably saw this fake-out coming, if not the exact details (I mean, who could’ve predicted the Skrulls would return?). For one thing, Mysterio is a well-known con artist whose supervillainy has always been the result of smoke-and-mirrors trickery rather than actual powers. It seemed unlikely that you would have to cross universes in order to find such a person. On top of that, Mysterio referred to the MCU as Earth-616. That sounds right at first, because Earth-616 is the classic multiversal designation of the Marvel comics universe (originally invented, like so many things in modern comics, by writer Alan Moore). But when you think about it a little longer, that’s actually wrong, because the MCU would obviously be a whole different universe than Marvel comics. Several things are different between those two continuities!
Back in the early 2000s, when Marvel started its Ultimate imprint, separate from the classic continuity, those comics got their own designation: Earth-1610. The MCU has taken inspiration both from the 616 universe and the 1610 universe, but as its own separate continuity, it would need its own number. Just because Mysterio was lying doesn’t mean the multiverse is false, but until we get a unique designation for the MCU (or the Spider-Verse worlds, for that matter), don’t get your hopes up for a meeting between Peter and Miles.