The “AR” in “AR-15” doesn’t stand for “Assault Rifle” though. It stands for “Armalite-15”. Armalite being the company that originally developed the modular firing mechanism that we all know today. Technically speaking, the only part that is legally classified as a gun is the actual firing mechanism that Armalite developed; Everything else (like the barrel, stock, and handle) is just add-ons and accessories.

So yeah, calling it an AR-15 assault rifle would be correct. Though there’s also the debate on what actually constitutes an “assault rifle”, as people seem to just use a “you’ll know it when you see it” rule for identifying assault rifles.

If the AR is for the AR-15, then you're mistaken on the meaning. That doesn't stand for assault rifle. It's for Armalite, the original developer of the gun.