So was Lozano referring to the Mexican consulate itself as being Mexican territory, in accordance with the common (though incorrect) idea that a consulate or embassy is foreign territory?
That interpretation wouldn't make sense even if the consulates-as-foreign-territory idea were true. If it were, Spokesman Lozano would have said "This consulate is Mexican territory". But he didn't, he said "This has been and will be Mexico" which sounds exactly like reconquista talk. And it's certainly not diplomatic. If this happened in a country whose leaders respected the sovereignty of their nation, this guy would have been expelled. The Consul in San Diego and the Mexican Ambassador in Washington would have been called to account.
Of course, that would be in a country whose leaders respected their nation's sovereignty, as opposed to ours.