I always joke about that to my buddy when I'm driving in his M3. Be the sunniest nicest day out, the wipers will randomly turn on going crazy.
I call them sunwipers.
Funnily this happens only in my model 3, not my X (I bought them before Elon went crazy). Both have automatic wipers on.
My gas car turns on the wipers sometimes when the sun shines on the sensor just right. Like a photic sneeze. Of course it cost about a quarter of a new Tesla