It is not out of the realm of possibilities that the heater caused this. If it did explode I am sure it started to expand first (since its plastic), which would cause the heater to pop out of the suction cup holders. If that is the case, and the heater exploded, it could have most certainly hit the POI as shown in a previous post. As to the above poster, anything hitting glass hard enough will break it, even plastic.
not when there is water in the tank. the viscosity of the water would stop any flying peice from building up enough momentum to break the glass with an impact point. its like trying to throw a ball when you are underwater in a pool. same thing.
now, if the tank was empty sure, but that just corroborates the likely theory that the tank had already broken before the heater exploded.