I think only games that were deliberately made available on one store should be labeled 'exclusive' in the news feed. 'Steam exclusive' in this section is misleading, as no agreements were made to this effect.
Topic on PCGamingWiki talk:News
Every act of publishing is deliberate. Going for Steam but not GOG or another store before Epic Games Store existed is an intentional decision. There are cases of games available only on Epic Games Store, Origin and Uplay that do not mention their exclusivity terms, if any, but they are still commonly regarded as exclusives. Relying only on pronounced exclusivity could significantly reduce the amount of games we can mention.
Personal preferences and biases aside, I think everyone would agree that having more stores and platforms to choose from is always better. As such, it would be hard to argue that over 7 years of PC exclusivity of Borderlands 2 to Steam is less notable than one year of Epic exclusivity.