Air Traffic Control can see whatever altitude is set in the window from the ground (Mode-S?) and apparently, they would have seen it changed from 38,000ft (the cleared altitude) to 100ft.
My understanding anyway, if an ATCO want's to clear that up, be my guest.
This is not so. The ATC tag will show the altitude the aircraft is cleared to (controller manual input processed by the ATC FDPS) and the actual FL and attitude of the aircraft (climbing, descending, level) derived from mode C.