"Anonymous source"
Yeah... anonymous sources are always on the money. They told us a bunch of stuff that turned out to be true in the past... oh no, wait, that was named, credible sources. Anonymous source means "our source wasn't credible enough for us to put his name in, so we printed what he said anyway in the hope of attracting some publicity".
Since it's pretty clear that retailers have sold out of the top WP7 phones (e.g. try ordering the HTC Mozart in the UK, or the HD7 in the US (not sure if it's sold out in the UK too)) it seems unlikely that the true numbers are anything like that low (unless the networks woefully underestimated demand).
EIther way, it's hardly a comment on the success of the OS. As Wired pointed out in an article earlier today, if you look at the numbers from the original Android launch (c. 100,000 devices on the first weekend (i.e. 2 days) 40,000 in one day really isn't very far behind...