Yeah. MDN is just a name, you learn what MDN means and you know it, like you learned what Apple means or what Windows means. "Mozilla Developer Network" sounds more like a description that you're supposed to interpret the meaning of, and one natural interpretation is the network for Mozilla developers, and another is that it's a network for people developing for Mozilla platforms, maybe to do with Firefox add-ons.
I'd maybe call it "misleading" more than "ambiguous" but meh.
And so what? It's not like they can fix the fact that there are old websites with outdated information on them, so people who are looking for what MDN means will find some outdated sources, yeah. Changing an initialism to a proper name takes time, that's not surprising.
I'd maybe call it "misleading" more than "ambiguous" but meh.