Sounds as though he might have just blocked off the overflow vent.
The fill level is controlled by a pressure switch via a small air pipe. The float switch is in the base and only operates when water leaks into the base.
If you use 3 in 1 or 4 in 1 tablets and rinse aid this often leads to overfoaming which then leaks into the base via the overflow vent. It is better to use separate powder, salt & rinse aid, Fairy Active Bursts are also quite good.
If he has blocked off the overflow vent and you do use 4 in 1 tablets then the machine may eventually leak onto the floor.
That which can be asserted without evidence, can be dismissed without evidence.