I also don't think Atalanta can beat Liverpool in Champions League this season if they meet again here and I have checked all the matches here but I didn't find any matches for both of these teams or did I miss it maybe because this season the format is different. But what you said is also quite logical that it is still not certain for Atalanta to repeat the victory if the team is faced with an opponent like Liverpool again in the current condition. Because Liverpool also have not been worse with their new coach this season and it has been proven in the early matches this season in the domestic league.
If it turns out Atlanta win Liverpool I may not be very surprised but then I will believe it's probably a lucky day for Atlanta, in champions league it's usually a very different spirit altogether because they know how prestigious the trophy is, Liverpool is a much very and experienced team in the champions league than Atlanta and this has been the reason Liverpool has been seen as the favourite. Atlanta have a sound confidence currently dues to the fact that they win the Europa and even this season they are starting on a good start but then champions league is really different.