Isis is my first beardie and she's just a year old so everything I know about brumation is just from what I've gathered on various other sites.
That said, it sounds like they go into brumation either when temps drop or just when their instincts tell them they're supposed to go into it. Maybe since his basking temps are a little low it's triggered his brumation instinct a little early. The sites I've read said brumation in beardies under a year old is rare but it didn't sound like it was completely unheard of. It also said some beardies go through it every year and some never go through brumation in their lives.
I'd still get the fecal done. Hopefully it comes back negative and your beardie just decided to get his brumation done a little early.