Do you think this was a false or what?

I have a Whistler 1788 sitting on the dash (on Highway mode) and driving at night on this stretch of road. I've not seen any LEOs in action at night on this particular stretch but tonight was different. Traffic was light as usual and suddenly, I got a momentary Ka 1 alert. It beeped a couple of times and stopped.
I thought it was a false because my 1788 remained quiet all the way to about 2 km down the road when I saw this LEO van parked by the roadside and I knew they were shooting from within the van (there was this warning sign near the van informing of police operations in progress). However, my 1788 was still as quiet as ever.

So guys, from what I described, did my Whistler really capture the radar gun or did I detect a false 2km before the LEOs?

It's possible. Were there any other cars around when the Ka alert when off? Reason I ask is because cobras will leak on Ka pretty bad and cause a brief Ka alert. If no cars were around I'd say it's possible you picked them up, maybe they were using instant on and decided you looked like you weren't speeding so they didn't hit you with it.

There were probably two or three cars around but I believe in my country, there aren't many people with RDs, so that is very unlikely. However, I forgot to add that when the alert went off, the vicinity on my right was an industrial area. Not sure if it was caused by auto-doors etc from there..

My main doubt was whether my 1788 was able to pick up an instant-on from almost 2km plus away since the LEOs were not in sight because the road was undulating and not straight...
Also went my 1788 went silent all the way after the brief Ka alert, that too made me unsure whether it did pick up instant-on