From what I gather, blocking an oil port is extremist and doesn't actually do anything but make life more difficult for the general population.
From that perspective I can agree with him. Blockading an oil port is an extreme approach to combating climate change. More sensible approaches would be figuring out how to lobby governments to tax fossil fuels and use that money to support renewable resources.
And people didn't think Trump had a shot back in 2016.
I live in a town that's split down the middle politically and I still see people flying Trump flags even after all the bs he has done. We even had a council member denounce pride month back in June at a council meeting. They think they are fighting the good fight.
Anyway, my point is that there are people who will see what Greta is doing, even if it benefits them, and still fight it because they think their side has their back.