If someone means “Debian and derivatives” then they should say “Debian and derivatives” not just “Debian” IMO, particularly when comparing to RedHat which also has a number of significant derivatives.
TBH I've always considered Ubuntu (and by inference its derivatives) more of an “inspired by” in relation to Debian, given it is generally closer to Testing then Stable and has many notable changes on top, more so as bigger changes have increased over time (snaps being so ingrained that they are almost required, for one).