residence vs source jurisdiction foreign, because, domestic, house

Palantir

My understanding:

Source jurisdiction taxes all income earned within its borders. German citizen temporarily residing in the US sells a house in US and pays taxes to US gov?

residence taxes all domestic and foreign income earned by a "resident". Germany tries to tax the guy on the US home sale because he is a german citizen?

Source jurisdiction usually trumps residence jurisdiction.

I'm getting mixed up on the "resident" part....should i think of the "citizenship" instead?