Ya, inner-Ukrainian operations don't count as "cross-border". 'Nuff said.
But Crimea isn't inner Ukraine... it's Russia. Duh.
De facto due to military force, yes. Very few countries recognize that border, however. The US, Europe, Japan, and the usual suspects have actively rejected the Russian annexation of Crimea. China and India have both been more ambiguous, but both have also shied away from formal recognition and active support. Only a handful of countries - Afghanistan, Cuba, Syria, Nicaragua, Venezuela, North Korea, Abkhazia, South Ossetia, Nagorno-Karabakh, and Transnistria - have definitely recognized the Russian annexation. Maybe Belarus if you interpret his words right; I would suspect Lukashenko is a bit careful about saying anything that could come back to bite him, hand-delivered by little green men, if the mood between Minsk and Moscow ever shifts again. In other words, as far as most countries are concerned, including those people themselves, it isn't a cross-border activity de jure.
Now, if you had Right Sector invading Rostov or something, that'd be something else, but it's rather patently obviously *not* a "duh" situation, and its rather disingenuous for you to assert it unequivocally as such. It's as "cross-border" as Ukrainian operations against the DNR (to borrow the tongue-in-cheek comment from earlier) or vice versa, and distinctly less so than, say, Russian operations against Crimea.