First CC and now this?! as a store mount instead... a reward

[Tsumdere]

yes I get that but why would 1 mount for blue be in before all the spells,armor and achievements

They've always added content in the game files before other things. Sometimes even by years. The Island Sanctuary ponytails were in the game files for literal years before Island Sanctuary.

Event sets are added sometimes 6 months in advance.

Shadowkeeper is being released along with Eden content. Releasing (or patching in) a Shadowbringers mount the same patch when BLU is going to be able to do Shadowbringers savages AND when previously they had gotten a mount for doing both 50/60 raids and now could do 70/80 raids... It's easy to see why people would believe it would be a BLU reward.