The explanation isn’t good but they aren’t talking about a normal supernova here, it’s a recurring one that I too never heard about earlier.
From Wikipedia:
> For other uses, see Nova (disambiguation), Novas (disambiguation), and Novae (disambiguation).
> Not to be confused with luminous red nova, supernova, kilonova, or micronova.
(Disclaimer: I have no idea what half of them mean, but I guess they are nasty things that can make a star brighter.)