Of course this always happen most times in football were a team that look more superior will end up losing against those teams that people always considered as the weak ones, this is why we can't possibly predict psg to win Aston villa just because they got liverpool eliminated. Remember Aston villa also defeat liverpool most times in there domestic league, that's to show that anything can happen in this match.
In the Champions League, no opponent should be underestimated by any team, especially when it has entered the knockout stages such as in the quarter-finals. This means that every opponent must be seen more seriously by any team if the team wants to be in the next round and win with enough aggregate goals to be able to qualify for the other round. Aston Villa is a fairly serious opponent and I think PSG also sees Aston Villa as a dangerous opponent because in the Champions League all abilities will always be deployed by any team without any fear, especially if the team no longer has a chance to become champions in its own domestic league.