Paul was just guessing or probably saw an old document at the time. NeoWin proved a conflict in his announcement, they said May, Paul said February.
I suspect that Microsoft would of course want to give XP 64 some time to be promoted before they start talking about Longhorn fully. WinHec in May 2005 will be the time to announce Longhorn, and talk about the beta being made available to testers in June of
Trust me on this one, June 2005 is Beta 1 for Longhorn.
I also read that Mile Stone 9 which is the last one for Longhorn Alpha will be March 2005.