They could, but they didn't. They got their powers from
spoilers:
end of spoilers Loki's staff that Strucker was experimenting with, as referenced in the movie and the prequel comic for same.
I don't know why everybody seems so obsessed with insisting that any MCU superhuman who's not an alien or recipient of super-soldier serum or user of tech like Iron Man must therefore necessarily be an Inhuman. Even on Agents of SHIELD, where the Inhumans have been getting introduced early and just recently got named as such, it's perfectly clear that some bonafide superhumans, such as the Absorbing Man, are not Inhumans. With Creel, for example,
spoilers:
being Inhuman is ruled out by the Diviner almost killing him until he used his power to adapt |
end of spoilers. There may not be mutants, at least named as such, but it's clear that there are many possible origins in the MCU, apparently including just being genetically different from other humans (i.e., a mutant by any other name).