Yes, it's pretty trivially easy to detect, even without fancy EW equipment. At one point I admin'd a college dorm's network, wifi/wired, and we didn't allow personal APs for interference reasons (you could run your own switch or router as long as it wasn't a WAP). Our run-of-the-mill networking hardware could find signals and triangulate them down to a couple of feet. A couple residents were flummoxed to learn that the "hidden network" thing doesn't actually do anything, which was hopefully at least a useful educational moment.

Any decent SDR can notice such things, presumably not to mention actual EW equipment. It's only really with sub-noise-floor gold code type stuff where a signal doesn't jump out on a waterfall spectrum chart, and even then it's generally fairly obvious at close range. I can only speculate as to why that didn't actually happen here.