Yeah that wouldn't be easy matches for both Atleti and Sevilla. But getting 4 loses from the last 6 matches isn't a good record for Bilbao, while Atleti only got 1 lose. Though Atleti got 3 draws and I think the draw result is fair enough for both team. Regarding Sevilla, they got 8 points from their last 5 games, and Real Betis only 5 points. I'm aware these statistics are hard to be taken as reference due to current situation, but we can't just ignore it.
I think that recent results doesn't means much after such long break. Maybe Atletico kicked out Liverpool from Champions league, but they are very vulnerable this season and struggling even bottom table teams. Loss against Eibar, draws against Granada, Leganes, Alaves, Valladolid, Espanyol doesn't looks impressive. They even got kicked out from Copa by 3rd league team.
Either it is fake news or that barcelona put in alot of money to not let this news spread further. Possibly third option, The infected had been taken care of
I saw these news on many popular websites in different languages and it got enough exposure. As I understand, players got virus without symptoms somewhere back in March or April and now they are completely healthy and tested negative. So, there is no reason to isolate them from training.