Emphasis on ten minutes... The main thing firefighters do these days is respond to medical calls. They do this because firefighters have plenty of medical training, and they're often the closest first responders to the scene.

What happened here is poison control wasn't sure if you needed help, so they told the firefighters to show up just in case. Three of them showed up because they weren't busy at that moment, they're getting paid regardless, so they might as well come out.

The reason why those firefighters weren't busy comes down to statistics: if you have enough firefighters to deal with the worst calls, most of the time they're going to have nothing to do. Fires happen randomly, so having enough capacity to deal with the situation 0.1% of the time forces too have lots of extra capacity 99.9% of the time.

Re: the stuff about wildfires, that's a very different type of firefighting, not relevant to firefighters in general. Usually an entirely different group of people with different training and equipment are dealing with wildfires. Don't conflate them.