Right, but this is a new development. Prior to the “humanitarian convoy” spectacle the bulk of the insurgents were Ukrainian citizens that got weapons from Russia. There were some Russian citizens and Kremlin agents mixed in, of course, but only now can we speak of regular Russian troops under the official chain of command invading.
Putin noticed that the “rebels” were stuck in Luhansk and Donetsk and not gaining ground, that is why he sent in the real troops.