Yes, if you live in South Africa were crime statistics are extremely high. The fact is that this is not the only question that is getting asked there are far more important ones, like trajectories. But, if this is the only question and you have lived in South Africa the answer will always be yes.
It is possible to hear a noise in the bathroom at night and think it may be a burglar. However before I grab my gun and shoot at the noise I'm going to check to see if my wife is next to me in bed. If not I think it is pretty reasonable to assume she is in the bathroom.
If I am like Oscar and hear noises from my bathroom late a night, I would assume it is a burglar. However, I believe that it could be handled in a non-violent way that would not kill someone if the person turns out to mean no harm, and would investigate it first.
I think it is obvious that some people may assume their is a robber in the house if they hear noises, even if those noises come from the bathroom. However, in my house, we would at least secure the known persons in the house, before firing shots. This is why guns are dangerous, because some people don't know how or when to use them appropriately. Overreactions are obviously dangerous.
No, it wouldn't cross my mind. If you have people or pets living with you in your house, you can expect to hear noises in the night. That's a given.
Also, consider how most master bedrooms are designed. In the majority of cases, the private bath is away from the bedroom entrance, which means you have to walk past the bed to the bath.
Why would a burglar break into a house, ignore the areas more likely to have high-value things to steal like silver from the dining room or electronics from the den, walk past people sleeping in bed, only to rummage in a bathroom? To steal toothpaste?
No, if you are married and you hear noises in your bathroom at night, it does not cross your mind that it might be a burglar, because the most obvious answer is usually the right one. And the most obvious answer is that it would be your spouse. He should have looked before shooting.