How it's possible a Family Share member can play my games while I'm playing other games?

[Gato Xikito]

It's just a doubt I just had, I recently closed Apex Legends and saw a family member playing one of my games with the "Library in use" tag under it. How?

[Ogami]

Apex Legend is a free to play game. Many of those do not trigger the "library in use" flag for Family Share so others can play a game of yours at the same time.
Not all free to play titles but many. There are some threads about it on Reddit.
Apex is one of the titles that can be played at the same time as someone else is playing one of your other games via Family Share.