Maybe the press release came out after Wikimania, but it was known to the relevant staff members at Wikimania.
I'm not on the board or the staff of any Wikimedia organisation, but at Wikimania one of the Union organisers told me in the presence of a board member that the board had requested the formal vote, and that he considered it a delaying tactic. The board member later told me that it's not that simple, that the board isn't basically anti-union, but that they're following process, and that it's complicated because there are some employees that are directly employed by the foundation in the USA, and others that are employed under local contracts in various other countries, through an agency.