Hard to tell. Could be - how hot was it? At 27C or more, my strong hive beards.
However, the truth is in the inspections. When did you last inspect? Any queen cells? They may just be bearding, or they may be plotting a swarm. If no queen cells, they are just bearding because of the heat and a full hive.
I recently spoke with a beekeeper who has a horrendous robbing problem. The hive was being inspected at 2 week intervals. I suspect that it swarmed and was weakened from that, and the swarm left the hive, undetected by the beekeeper. That hive is being robbed now, probably because of a nectar dearth in that area (very hot weather for quite a few days) and very few original bees left to defend the remaining stores. That is the reason I am asking about inspections.
There are some myths out there that hive inspections are not needed very often. I disagree profoundly, unless we are talking about a new package or a nucleus in only one box. Those can be left alone for 2 week periods until they have filled a deep. For established hives, during a nectar flow, I think inspections should be done at least once per week (searching diligently for hidden queen cells), unless you are willing to risk losing bees and honey to a swarm. Just my humble opinion.