Counterpoint,
this exists and has stormrider in the name so clearly the heroic mount is actually a dwarf.
eyebrow wiggle
In all seriousness, creative crack theories can be cool but your insistence on this one is weird. The existence of the dwarven storm hammers, explicitly linked to the term 'stormrider', when dwarves with hammers are known for riding - wait for it -
gryphons would seem to indicate that the mount is probably a gyphon.
Could it be something else? Sure! But finding some random mob by plugging 'stormrider' into wowhead and shrieking '
eureuka!!' is not the smoking gun you seem to think it is.
As others have said, it's the Blizzcon swag which is distinct from the xpac collector's edition. They'll likely reveal it in the lead up to Blizzcon to increase the sales of whatever the not-virtual ticket bundle is.