No, it is not "fair to say they aren't selling all that well" when as far as anyone knows, they could be a complete flop, or the sales of Homepods could be meeting or exceeding Apple's expectations. On the earnings call, Tim Cook said the category was doing extremely well and simply said that they had started shipping the Homepod during the quarter. Being on sale for only a couple of months in just three countries, with key parts of the software yet to ship, why would anyone expect him to say "The HomePod sales are meeting our expectations" ??
Again, the Homepod might be a complete flop, and it's understandable people will guess in the absence of facts, but the repeating of rank speculation as fact, without any facts is why nearly all of the pundits claimed the iPhone X was a complete flop and were humiliated when it turned out the facts were it was a great hit.