Clip's dimensions automatically matches composition's dimensions

[swag user]

Whenever I put a video onto new composition it changes it's size to match dimensions of the composition
(picture 1)
But when I open the clip as it's own composition it stays in its original dimensions (picture 2)
Also when I copy the clip from it's composition (picture 2) and paste it to a new and different sized composition - it changes too (like on picture 1)
How do I make it stay in it's original dimensions?

[Mylenium]

You are likely not considering things like pixel aspect ratio and that's why your footage behaves this way. Check your footage interpretation and comp settings.

Mylenium