Buxton did start to get more hits, so in that sense his bat heated up, I guess. But he had one walk in August, versus 13 strikeouts, in 12 games, versus AAA pitching.
This should be about Buxton's long term success, and I don't think he showed the plate approach in August necessary to build a base for sustained MLB success at the plate. And I suspect the plate approach he was showing in AAA most likely would have led to MLB pitchers, yet again, carving him up in September, even with expanded rosters.
Maybe, maybe not, but I don't think it's as cut-and-dry as some make it that Buxton's AAA batting line last month was definitely deserving of a call up. Small sample size regardless.
As an aside, I noticed that he hadn't attempted a stolen base in August. Might lend some credence to the notion that the wrist or another lingering injury isn't allowing him to play full speed. Might be the team trying to keep him healthy. Might just be a coincidence.