Not enough room or a pre-swarm of bees?

We are new with this; we started this beautiful adventure on June 28th of this year. Everything is going pretty good, the hive is strong and not aggressive at all.

We are supposed to add a new honey super tomorrow, but we noticed this behaviour this morning and this evening (see picture).

Supposedly, this is normal because it's been very hot lately (no rain for the past 10 days), and this behaviour is supposed to reduce the temperature?

What do you think? Are we missing something? Are we doing something wrong?

Thanks for your opinion and your help!