This is understandable if we know that Betelgeuse is in a filament, and we are seeing it with a light path that grazes down along and into the filament.
First, what they are not seeing: Betelgeuse is not changing in size. They say it's not changing in brightness,but it's changing in size? So it's getting hotter? No, they don't see that either. Mainstream or EU, you can't have a star getting smaller in size, without getting dimmer, unless it kicks out more light /unit area (changes spectrum).
Remember the work of Ed Dowdye Jr? He showed that light was bent as it grazed the sun. Not because of gravitational bending of space, like the mainstream thinks, but simply from passing though all the plasma right at the sun's surface. Bent in the direction of increasing plasma density.
Well,if the plasma in a current filament does the same thing, and we see Betelgeuse with light that leaves the filament on a grazing path (we are looking mostly along the filaments edge), then light from Betelgeuse is bent towards the filament surface. The changes in path length from one side of Betelgeuse to the edge, are merely a function of how much plasma we are looking through at the time.
So Betelgeuse's size and parallax distance are both going to be skewed by this viewing angle through all that plasma. (even a low plasma density filament gets to be a lot of plasma when you look down through it

They measured the size of Betelgeuse by interferometry, and located the bright spots on it using the same method. Of course,interferometry depends crucially on the light path. The mainstream knows this, and has developed ideas to test for warped space or gravity waves using interferometry. But if Ed Dowdye is right about plasma bending light, then all their measurements are in question. Looks like Dowdye did for interferometry, what Arp did for the redshift/distance scale.