I’ve never really experienced the “butteriness” that people speak of, since I rarely drink chardonnay. Some note it more in the context of a flavor profile, but I have heard others (rpm and Peter Wellington) not it purely as a mouthfeel. I definitely not get any buttery flavor profiles. As a mouthfeel, maybe some butteriness, just in the way it ever so slightly coats the mouth. I would not consider overly buttery in that regard.
My “aha” moment when I identified that was while consuming some of the Nicholson Ranch chardonnay that was offered here a few years ago - early in both my wine-drinking and wine.woot days. (Those coincide pretty closely, right about the time I started to feel a need to expand by Trader Joes shelves.)
I recall that as I was finishing a glass, I had a sensation in my mouth that was similar to the sensation after easting a slice of toast, overly-buttered and with apricot preserves.