Firefighters struggle lifting 24.5 lbs?
I'd guess that most people can lift 12kg. But lifting and wielding ain't the same.
12kg shouldn't be much of a problem for most people, if the weight comes in the shape of a dumbbell and stuff ain't on fire.
But wielding a toddler-sized implement awkwardly in front of a fire while you are a bit panicking yourself, might be a struggle for many people.
Especially since you probably never practiced this, and you might even have to hold the thing one-handed, so you can aim with the other hand
[1] scroll down to table in https://blog.qrfs.com/66-ultimate-guide-to-fire-extinguisher...
Also you are not benchpressing in optimal position, you need to hold it at an awkward angle.