How does Garmin choose between indoor cycling and virtual cycling

I have activities that are both 'indoor cycling' and 'virtual cycling'  and I do not know the difference. Garmin seems to assign them at random, which makes it hard to see all trainer rides at once.

Background: I ride indoor for most of the winter on my regular road bike attached to a Saris H3. I virtually ride courses that I have loaded onto my Edge 830.

Any idea how it decides to call the activity indoor or virtual?