Frites aren’t “considered” to be a Belgian invention in France. They’re known to be a Belgian invention everywhere.
As for French Toast. In French its called pain perdu (lost bread). The UK and Ireland tend to call it eggy bread. Though its got a bunch of different names. So far as I’m aware the US calls it French Toast because what we make is generally derived from the French approach. Which involves sweetening the egg mixture, cutting it with milk or cream, vanilla extract and generally treating it like a custard base. Where as the UK and Irish method more traditionally involved just beaten egg. So its definitely got something to do with France. But the dish more generally is just an incredibly common way of dealing with stale bread.
