I looked it up on the Kickstarter site and found the details:
Also, we discovered during the final preparations for shipping that one tile for the Outer Belt expansion (the Blish Expanse tile) was not included in the box. Again, this only applies to the full copies of the Big Box, not the Galactic Pack. Game Salute is already working with the factory to print the Blish Expanse tiles.
Rather than further delay delivery of Alien Frontiers Big Box and Galactic Pack, we will be shipping now so you can enjoy the game (you do not need the Blish expanse tile to play the regular game, just the Outer Belt expansion). We will be sending 1 Blish expanse tile to each backer who receive the full Big Box (1 for each copy of the Big Box that you receive). The Blish expanse tile will ship out worldwide from the US by post, once we’ve received them from the factory in the coming months.
You do not need to complete a replacements request for the Blish expanse tile. We will automatically ship it to the same address we sent your reward package to once they arrive from the factory.
So I guess they got their lists wrong as I received the email as well and had only ordered the Galactic Pack...