Since when did geography become a protected class?
Technically the Constitutional protections of geography were included in the ratification of the constitution in 1789. Additional protections were added when the 14th amendment was ratified.
The only question in this case would be whether the use of the Government owned and operated stadium by the Seahawks would require that the Seahawks provide the same protections to out of state visitors that would apply if the government itself were selling the tickets.
In this case since the rights of the Seahawks are in the form of a leaseholder to the seats, any sale of tickets would be in the form of a sub lease of government property and as such, the Seahawks would be held to the same standard that would apply to the State.
Since the State could not so flagrantly discriminate against the Citizens of California, the leaseholder to State property cannot do so either.