Yeah, after wasting eight years of my life doing Latin at school I understand the basic etymology, but I’m confused because the English meanings aren’t very close. Your careful phrasing manages to get the word ‘hold’ into both of them, but ‘someone who holds a lease’ isn’t a very natural-sounding definition of ‘tenant’, and the notion that most people who make this mistake are familiar with the paradigm of teneo feels rather tenuous (plus ‘tenant’ noticeably isn’t a Latin ending, it’s apparently Old French, though transitively descended from teneo). You don’t think it’s more likely, if anything, to be that they just sound similar?