Toasts are bad UX for an app which is used in a casual context, yes. The odds that an untrained user missed them and becomes confused are quite high. But there is nothing wrong with a toast in a pro app. The pro user will get used to where feedback comes from on the screen and find it is second nature to notice the toast. In practice, there are very few UX principles that generalize across every interface.
The end result is usually that I've been distracted for no reason.
In a casual app, none of this matters as much.