It had been warmer for a few days, but had been cooling off and getting rainy again. It drizzled some overnight on Wednesday night, and most people were in long sleeves with layers. For many of us, 50's is cool, and it's significantly cooler down by Lake Hodges and in the far side of Westwood (in the area the other assault occurred, etc.) than it is even just a mile away at the freeway. As in, it's consistently 5-8 degrees different there than the freeway and what shows as the registered temp for RB. And by late afternoon it'd drop even more.
So a sweatshirt is certainly not out of the question for last Thursday...but SO many people run/bike/hike/walk/horse through the trails, plus the migrant workers who live and cross through that area, it really could be anyone's.