There are people who would interpret a column of military vehicles entering a sovereign country's territory against the will of the legitimate government to be an act of war. There are people who would interpret destroying that column of vehicles as an act of war. There are people who would conclude that when hostile countries engage in successive acts of war against each other, a de facto state of war exists between the two. Or they could just understate the situation and describe it as a significant escalation.
Actually, Putin’s been waging an illegal war against Ukraine for some time. As for the Ukrainians, if reports are correct that they destroyed Russian military entering their country, then I’d call that an act of self defense.