I am not certain to understand it all .
If Schaerbeek City Hall told you he died in Gent , than he did died there ...they know..why shuld they tell a lie ? That death record is in Gent than ...
What is it you really want ? What death record ?
Even if Frederik died in Gent , it is possible that he was birried in Brussels i don t see where the problem is..;It s common and not unusual