I feel that in terms of the actual what's-placed-in-it they are very similar, with AD&D winning out a bit in that there's plenty of stuff (like mind flayers) that came into AD&D after it branched off from the basic/classic line, but less that counter-examples from the other side. Tonally (or as Voadam points out, artistically), I think there is something that B/X has that makes it feel moreso like what Deganawida was talking about. Probably in the empty space/absences. There's less discussion about building a working world, of limiting characters (from caster spell fizzling on hits to the 1e DMG admonitions against letting the Thief get away with anything like trying to climb wet surfaces), of grounding the game in a semblance of realism. It's all minor, arguable, and of course the two converged again as the Mentzer set added a bunch of analogue to what AD&D was doing (and the settings for each took off into the bizarre, with Gazateer-era Known World and AD&D settings like SpellJammer, Dark Sun, etc. took dialed all of this up to 11), but I do see what I think they mean.