Another possibility: If you have Seasons and the Prank Day is in effect, from my experience there's way higher chance another sim could have persuaded that one to go streaking.
My own sims might do that autonomously anyways since I have idle chatting disabled and mods affecting autonomy depending on traits (so Goofballs are especially aggressive with mischief) but during Prank Day some sims who like never do mischief, might as well. (Learned this the hard way when Vlad's husband apparently persuaded him to go streaking in the middle of a sunny day and I only noticed when he only had like a sliver of vampire energy left. Trent's apparently planning Vlad's demise.)