I do, because that’s not the only way of inducing the bug - it’s just a rather convenient way of doing it.
Suppose global site CSS on an installation does exactly the same thing - would that be discounted as well?
Or turning my monitor to portrait mode and using the default CSS on here, which would result in exactly the same problem - would that be discounted?
There must be some way of detecting that the last item currently displayed isn’t actually off-screen and to load the next batch until the last item loaded is off-screen?
We can play Hyperbolic What If™ if you want, but what I’ve presented here isn’t it.
But to answer your question? Yes, it is your bug. If you’re loading when the last item comes into view, but you don’t load if the last item is already in view, that’s Not Expected Behaviour.