It, like most copyright laws and fair use, is a gray area.
There's a chance they could be flagged, silenced, or blocked in some countries/ devices, and there's a chance that nothing will ever happen to them. There's no way to know and, unless you're willing to go to court and fight for the right to have random background music playing, it's generally best to simply play it safe and refrain from using music you don't have the proper written rights to use.
With all of that said, there is a decent chance that, if it were to go to trial, the courts would rule in your favor as part of fair use, but the risk, time, and financial burden is hardly worth it without assistance... such was the case with Lenz v. Universal Music Corp.