Can’t say for certain but likely they were just rotating the squad. The Russian played in goal against Flamengo and apparently saved 4 penalties in the shootout. A different reserve keeper played in the French cup at the weekend and Chervalier and the other keeper were on the bench. Seems like two goalies on the bench is all the rage!
It's more problematic than this - Zabarnyi (the CB) is Ukrainian, and doesn't really want to have anything to do with Safonov which makes communication in defence a little tricky... so they'll keep playing Chevalier, or play Safonov and drop Zabarnyi.
It's the sort of squad politics that is refreshingly absent from Villa at the moment.