This seems to be hard for you so let me help you out.
He's a politician even if he "only got 4% of the vote" and when a politician burns the EU flag he makes a strong statement.
And I would be interested what he said in that video I got a feeling it aint pretty ^^
What he says was just a typical bullshit like: "we are burning flag of the hostile organization, that is not the country yet fortunately do there wont be any diplomatic incident"
The guy is most prokremlin, antivaxin, antijewish, radical catholic, monarchist.
Really the most crazy guy in our country politics

I mean: when you tell to the people that all would be rich but jews keep stealing our money, you will get *some* public support.
Who doesnt want to be rich after all? And the guy offers a simple solutions: lets just stop jews from stealing our money.
People like simple solutions, they can understand that.
With such views you can get 4% in Poland, or win elections in Germany in 1933

There are some tensions of course, one is about coal. Polish miners want to keep digging searching for coal. They need to dig 1km deep to get some coal here in Poland, because all closer coal was already used up.
Miners protest, they want more money from the government.
On the other hand planet is burning, and EU would like to stop global warming before its catastrophic.
The people dont always believe science, they dont believe in vaccines, they dont believe in global warming.
Because these are complicated matters, and they dont like to overthink, they prefer the easy solutions, and they dont want to give away any of their luxuries.
Populists provide the people with easy to understand solutions and explanations:
"Why arent we rich?" "Because EU is stealing our money."
"Can we just keep mining coal forever like our ancestors did?" "do it, there is no global warming"