Lens is far away from being the best team in that group. Also, the best team never really is the one that won a single encounter between two teams. The best team would be a team that is at the top of the table after 20 or 30 games. But it is exactly the fact that there are only a few games and there is some randomness involved of course and since they won their home game against Arsenal already, it is not impossible for them to survive that group. They are in a great position and definitely in a much better position than they expected while they had this horrible start into the season. From now on everything is possible for them thanks to those 3 points against Arsenal.
That's what I said before that Lens are not strong enough to be favorites to qualify for the next round because there are many upcoming matches that can change their position in the standings table. I think Arsenal will not allow other teams to disrupt their progress in the Champions League this season. Arsenal has been very strong this season, they must be able to concentrate well in every Champions League match.
Let's just wait after the team finishes the first leg in the Champions League this season. If Lens can maximize the opportunities that exist, maybe we will see another surprise this season. But in the second leg, I'm sure that when Lens come to the Emirates stadium, they won't be able to win that match.
But we have to admit that Arsenal has still two games to go in the group that should by no means underestimated and could still get them into trouble if they lose them both or do not win them both to be more precisely. The game away against Sevilla and PSV Eindhoven will be harder than many may think I believe. Beating Sevilla in their home stadium has turned out to be a very diifficult task and despite the crisis that Sevilla is going through, I expect it to be hard again this season also for Arsenal. PSV has been beaten 4-0 in the first game, but lots of things worked out well for Arsenal. It wasn't as one-sided as the final result may suggest.