"Protecting Donetsk and Luhansk" literally means sending troops into Ukrainian territory to fight against the Ukrainian military. That's called an invasion.
EDIT: though the wording might still be significant. If the question is worded "Should Russia support the sovereign, Russia-aligned republics of Donetsk and Luhansk", that might poll significantly differently from a question that's worded "Should Russia invade Ukraine" even though both mean the same thing. Just like how >50% of Americans answer "no" to the question of "Should schools in America teach Arabic Numerals" because they're misled by the question, not because they're opposed to teaching people about numbers.
Donetsk and Luhansk have declared independence, and Russia has recognised them. Secession is not a new phenomenon; Texas seceded from Mexico. Several regions seceded from the former Yugoslavia, and were rapidly recognised (and reinforced militarily) by western countries.
I think it's perfectly legitimate to argue that Russia is not invading Ukraine, but rather supporting the Donbas republics. I mean, I don't agree; and I think there's a fair chance that Russia will invade Ukraine, and install a puppet. But they haven't done it yet. I suspect that for the next few weeks, they'll restrict themselves to air and missile attacks on Ukrainian military installations, with troops-on-the-ground restricted to Donbas.
Beyond a few weeks, who's to say? No plan survives first contact with the enemy.
