The first thing I thought is "but, what D&D do they play?"; because D&D has changed over the years.

Turns out the game started as the D&D of the time (AD&D), with more or less house rules; and then moved on with some "homebrew" rules that are still familiar to D&D players.

I mostly tend to say I played D&D back in the day, but the truth is, I only played actual D&D on one short one-afternoon session. I played other games instead (LoTR Middle Earth, RuneQuest and Vampire), but D&D is what people mostly understand I guess.