Trump has a pretty fair sense of history, being 69 years old. This concession seems to come for a reason.
Russia has bad corruption problems, and America has lately been no paragon in that department either. Trying to be a superpower when you have super-rot is ultimately a vain pursuit, and Putin knows it. The rot has to be addressed.
I took it as euro-snobbery myself. Utilizing a word which means bright in a gaudy sense, but putting it a context to interpret as “bright” in an English language sense as “intelligent”. I remember getting that sense at the back of my neck when he said it, that it was back-handed, and that turned out to be right. He equivocated. See, this is us being tone-deaf American clods... Don’t you know...!