Can you explain this contradiction?

Insects may not be “warm blooded”, but they are most definitely able to sense ambient temperatures.

They are also most likely capable of noticing dehydration, so possibly they are simply responding to that. Also, they may not be able to ‘feel’ temperature differences in the same way we can, but that doesn’t mean they don’t have a mechanism to sense temperature. A subtle difference but possible, but you’d have to ask an entomologist.

A thermometer’s temperature is also dependent on its environment’s temperature.

That doesn’t mean it cannot sense its environment’s temperature.

They also are looking for moisture. They still need to hydrate.

Ants are cold blooded, so the only way they can regulate their temperature is to move or change their environment.

They don’t “know” anything.
But they are pre wired to do certain behaviors under certain circumstances that present in their environment. Such as getting too hot, or being dehydrated.
As long as they confront the circumstances they are pre wired for, they have a chance.
If a challenges emerges that they are not wired for, they are at risk.

Even if they don’t feel it, their instinct tells them what to do or search for. For example if you grab an ant and rip off one of its legs, it apparently doesn’t feel the pain like you or I would, but it definitely knows something shitty is happening.