Hmmmm
I the article they say the luminosity did not change a lot..
That means the temperature must have gone up (to compensate for smaller radiation surface), which means there must have been a significant change in spectrum. And that would have been noticed for sure.
And, Betelgeuse is known to be a variable, so..
Also, the photosphere of stars like that is not very well defined, so it is very hard to say where the star ends and space begins..
Hmmm ....
