The problem with electric motors is back EMF, not so much RF - motors don't spin that fast. (Switch-mode power supplies
do switch that fast - into the hundreds of kilohertz - which is why cheaply made and thus poorly suppressed ones do tend to produce radio noise that you can hear, in harmonics at least, in the lower AM band. It'd be rare to find a tool motor that spins much over 30K RPM, and even that's on the high end.) So the noise is too low frequency to qualify as RF, but you're still dumping inductive voltage spikes into the supply, which can destabilize other equipment on the same circuit or one nearby - in this case, while the neighborhood concentrator might not have been (probably wasn't) on the very same circuit as the trimmer, it probably was on the same transformer, or else the circuits ran parallel in a conduit somewhere and the noise was getting capacitively coupled into the concentrator's supply.
This wouldn't be a problem with a battery-powered trimmer because it isn't connected to the aircraft's hotel supply - or if it is, it's through a wall wart, which will contain a transformer and at least some suppression circuitry, which will dissipate any EMF that makes it out of the tool. And in general, the way you suppress this kind of inductive noise is with capacitors and chokes, which any reputable manufacturer of a line-powered motorized tool will include in the design. But there are a lot of disreputable manufacturers out there, too.