This is a thing I've seen show up in D&D video games since about Demon Stone. Levels of various monsters being modified to allow for appearing in the plot as is appropriate. D&D tends to be designed that you start off with relatively minor local affairs and build up to the epic things, but a lot of computer game writing is counter to this with the idea of throwing the epic stuff in right at the beginning to see and then put you in lower level stuff until you can work your way up to dealing with that epic stuff.

I'm kind of okay with it in a tutorial because it allows for the epic opening they wanted. I'm also semi-okay with it for titles like "Archdruid" because I get a bit ehhh over titles being tied to a meta-statistic like level. If there's a druid grove it will have an archdruid and if the highest level person is level 4, so be it.

As for a 4th level red dragon... If the "levels" are more equivalent to "CR" from the tabletop, that would be a hatchling. Which would be medium...too small to ride. I think the dragon we see is large or huge so it would be Young or Adult...which would be CR 10 or 17.

But I imagine they are going for the dramatic conclusion to each chapter. I again think this comes from the difference in story pacing video game writers are used to as compared to the tabletop game is designed for.

Black Isle, Bioware, Oblivion, SSI and the like feel like they were designing toward tabletop pacing more than typical video game pacing. Where as the studios that have been designing D&D RPGs since then are more like they're coming from the video game side to the D&D projects. I don't particularly care one way or another. Either can work and I drop a lot of expectations for video game adaptations anyway.