I feel like I read somewhere that it’s kind of a way to see if you’ll incriminate yourself
That’s exactly what it is. If they’re asking you that question they want you to admit to whatever it was (speeding, etc) so they don’t need evidence and you can’t fight the ticket.
Play dumb, but be polite.
“I’m not sure, could you please tell me what you saw?” Or something like that.
Remember, just like in an accident, don’t admit fault. You can decide later if you want to fight the ticket, but if you admit fault then and there, you lose that option.