I'm not sure on the $50k part but they have been doing pop up roadside check points for many years.
Here is what I found on the state web site.
If you fail a roadside smoke emission inspection conducted by MVC in conjunction with the New Jersey State Police, you will be subjected to the following penalties: $700 for the first offense (reduced to $150 if paid within 45 days and with proof of repairs) $1300 for the second offense (reduced to $500 if paid within 45 days and with proof of repairs)
We do have pretty strict Air Permits that go as high as $50k, those are for stationary gen sets and the sort. Emergency power and running on Air Quality days. You have to work pretty hard to get up to the $50k level, I can't find anything that high for vehicles in a bunch of stuff I looked up.
NJ DOT and the NJSP has had mobile inspections for trucks for more then 20 years, they use a few 24' trailers all set up with mobile scales and the sort, they recently added the emissions element.
Here is the new program that they most likely were testing out prior to full roll out...
https://www.state.nj.us/mvc/inspection/dieselemission.htm
We are not a truck friendly state, we closed all rest area bathrooms many years ago, we have almost no parking for big trucks along I-80 and I-78 from PA to NYC.
The north to south NJ Turnpike has rest stops for trucks, but it's a pretty sad state for trucking.
Years ago they enacted a ban on big trucks on a bunch of state roads except local delivery. It was a complete cluster at the time. That lasted only a few weeks then they went with a 102 wide ban and doubles all have to run specific routes.
It's a nice state to live in, but you do have to deal with quite a bit of BS.
In Jan 2020 Forbes released its 14th annual "Best States For Business" ranking. NJ was #39. No surprise there.
I can go on, but you get the point.