Well, North and South America are two different tectonic plates[1].

[1] https://www.usgs.gov/media/images/tectonic-plates-earth

They really aren't, there's no objective way to divide the world into exactly 7 continents (or 6) using geology.

America, Afro-Eurasia, Australia, Antarctica

I can count 4

Based on what?

Based on being large landmasses

Potentially any island is a continent if your cutoff is low enough

Europe says hi.