Curious absence of humidity in basement
A smaller (non-oversized, might be another way to put it) air conditioner can in fact be much better at removing humidity than an oversized unit that runs for short periods and shuts off. That is, in fact, one of the problems of &quot;going big&quot; on an air conditioner - it keeps up on the hottest days, but most of the time it means you're danker than with a right-sized unit.
As noted already in comments, the roof (and perhaps gutters, if?)  or the climate may also be helping to reduce the moisture immediately outside the basement.