Literally all keyboards are mechanical, what’s the alternative? Organic?
The term is used figuratively, not literally.
Buckling spring keyboards count, rubber-dome and scissors don't. There's no overarching principle here, if there is, it's how they feel under your fingers.
It’s not a precise category. But I’d even go so far as to say they are the type specimens for mechanical keyboards.
Yes, most products in the category use Cherry-type switches, but Topres are definitely considered mechanicals and they combine a rubber dome and a spring.