I was driving today and noticed the fan was staying on, which is unusual, temperature was a little high, usually halfway between 40 and 80, now creeping up to 80. I pulled over popped the hood and saw that coolant was boiling in the reservoir, but barely, it stopped as I noticed. I checked oil which was fine. I started to drive home watching the temperature and it kept creeping up til close to 80 and the boom, the lower hose from the water pump blew off the pump. I pulled over and got a tow.

What do you experts think happened? The temp gauge never showed close to red line.

Thank you in advance!