Not necessarily. How would they guess "this thirty-something man is actually several hundred years old"?
Except they're not. We are told that on this very page, they're going to test various measuring devices until they find one that works.
The point is there are an endless number of potential explanations. There are no guarantee they'll figure out what is deal is.
Not really, once they've managed to detect him, Higgs is irrelevant.
Not really, this is a world where random mecanic #562 can do this
(pay attention to the vat and mug).