"My gasoline car engine
calls for 5-w20."
Sounds like you have a fairly recent Toyota.(G)
"I would not risk putting diesel oil
in my gasoline engine
The only question is whether the oil
is "S" rated for "spark" engines, or "C" rated for "Compression" engines. Most, if not all, Rotella oils will carry a fairly high API "S" rating and surpass all OEM specs for gasoline engines.
But along with your 5w20 SAE oil requirement, the odds are your engine calls for an API SM or newer rating as well. That's what you'd need to check.
I'd bet someone got distracted and when they got to wherever, they said "Oh ****! Where's that bucket of oil? Well, I'm not going back to spend all day looking for it."
ADHD seems to be the new norm these days. Certainly are enough people trying to make sure we can all suffer from it.