That's nothing to do with the actual speed limit but with the EU limiter law. If VOSA catch him exceeding 56 (90kph) they will slap a prohibition order on the truck and the tacho and limiter will have to be recalibrated. He can't personally be done for speeding however unless he exceeds 60mph.
I know this because the other half got one yesterday. He was pulled over into one of the routine testing stations that VOSA set up and they proceeded to plug something into the tacho head that can apparently tell what the limiter is set to (something to do with setting the engine running at limited speed in top gear and seeing what it revs to - I don't really understand how it works). According to the device his limiter was set to 91kph (dispite the fact that the truck actually won't exceed about 53mph or 86kph which can be proven from tacho chart records and the fact that he gets overtaken by pretty well everything else on the road

), so he now has 10 days to get it recalibrated and inspected. More than likely the device VOSA was using was out of calibration or something else was amiss here, but his employer will still have to fork out for the inspections.
So I can understand why his manager is a bit sensitive about it - unit off the road for half a day + calibration and reinspection costs...