This is not a Dyson sphere as it is not enclosing the star. We could not detect a Dyson sphere with this kind of telescope. I suspect this is extreme variability of the star’s output.
Types of Variable Stars: Cepheid, Pulsating and Cataclysmic
by SPACE.com Staff
(snip)
“Other pulsating variables include RR Lyrae stars, which are short period, older stars that are not as large as Cepheids; and RV Tauri stars, supergiants with greater light variations.
Long-period pulsating variables include the Mira class, which are cool red supergiants with large pulsations; and Semiregular, which are red giants or supergiants with longer periods that can range from 30 to 1000 days. One of the best-known Semiregular Variables is Betelgeuse. Irregular pulsating variables have also been identified. These are usually red supergiants, but very little study has been done on them.”
Maybe they’re starting to build a Dyson Sphere. Takes a while, ya know.