I have no direct experience of iOs but according to the post it's as you wrote. It could be an app that needs the camera once for some sensible reason, then it can use it forever when it's active even if it wouldn't need it from the point of view of the user.
Isn’t the definition of an active app, one that is open and in the foreground?
The minute the phone sleeps, or the app is put into the background, access becomes more at Apple’s discretion.
I’d expect an app running in the foreground to be able to keep using the camera as long as needed..
Or is your point more: allowing once allows it every time the app opens, with no option to repeatedly prompt?