Which Detector Would Make My 8500 X50 False Alarm?

[b4z]

Background: Owned an Escort from 1983 to 11/87 when it was stolen. SC raised the speed limit the following year ,so I never bought another radar detector.
Being 21 years without a detector I am not up on the new stuff, so forgive me if this is a stupid question.

I bought a X50 as a present to myself prior to Christmas.
In january I was driving from Chas. SC to H'ville, NC entirely on I26.
Got to the the I95 interchange and a bunch of vehicles were merging and
my Xband went off full on- and stayed on. After about 2 miles of this and not seeing any cops I thought something was up.
Since I had slowed down, the vehicles that had merged were now starting to pass me slowly, and for some reason I took notice of a F150 with a detector on the dash.
As he came up the Xband stayed on. He passed and got about a quarter a mile away and it stopped. Except when I got to the top of a hill it would get worse.

I figured that it might be his detector that was setting mine off mainly because it was xband I don't think that is used very much anymore.

I got my courage up and stepped back up to 80mph, passed him and the escort went crazy on Xband, once I put a half a mile on him it went away.

What the heck kind of detector was he using to cause this?
It really messed up my time to NC.