If I get an email to my school account from a certain college, does that mean they’re interested in me?
No. It’s marketing.
The colleges may have some idea of your test scores, or at least know that your scores were above a certain level, if you agreed to be contacted when you signed up for the SAT/ACT. But otherwise they probably don’t know anything about you, and it’s likely that they sent the same message to thousands (maybe tens of thousands) of other students.
it means they’ve used the cheapest means of communication possible, an email, to try to build your interest in applying. Didn’t spring for a faux letter from the dean, a brochure or a catalog, so you’re not even worth that much to them at this point. Colleges like to fan the number of applicants so they can be appear more selective in the stats; that in turn makes even more kids want to apply because they want to go where everyone else wants to get in.