The Grinch saw all the commercialized trappings of Christmas and hated it because that’s what he thought it was all about. It was only after he saw the Whos still celebrating even without the commercialization that he understood the “true meaning of Christmas” and wanted to be nice to them instead.

The anti-capitalist part was his motivation in the first place. If anything, returning the stuff was an erosion of that belief (I don’t think it was – I think it was more neutral than that – but if you had to debate it through that lens the point could be argued).