I feel that selling buildings should indeed count towards the supplies and coins gained.
Its a normal part of play to sell buildings off and one gets a small return of coins and supplies at such a moment, so I see no reason why that should not be the case during events. Its not a bug to get those back, so its a legitimate way of adding them to your storage.
sure, one can do it on purpose, but since one only gets back 50% at best it forces players to take a loss. If someone wants to do so, let them