(Alleged) anti-capitalism and marketing are not mutually exclusive.
Banksy has an eye for publicity, from selling his art for $60 on New York’s streets [1] to parading a painted packiderm [2]. Whether it’s to sell his art (which it does), sell his name (which it also does) or sell his ideas (which it does, too) is orthogonal to it being clever and effective marketing.
Yes, in this case Banksy is clearly trying sell his name and idea, I can't dispute that. But the comment I replied to implied it was done in partnership with Sothebys in order to increase the value of his art and therefore make more money from it. At least, that is how I read it. That kind of 'marketing stunt' is one that just doesn't fit into his MO which makes it hard to believe.
It was the very last peice sold. If it had been sold at the beginning or middle, odds are the whole auction shuts down, at best the tone changes. This was calculated.
Someone had to put in new batteries in it and they took it off the wall right away to show that there was no cord. It is possible the auctioneer himself was not in on it but others had to be.