My water is boiling too fast

Adding a starchy substance such as rice or noodles to boiling water increases the surface tension of the water. When it's just plain water boiling the surface tension of the water can't hold back the force of the steam rising and the bubbles burst. Starches increase this surface tension making the bubbles more elastic/pliable (essentially creating a foam), thus requiring more force for them to burst. This makes the bubbles last longer which allows them to build up and eventually boil over.

It's more likely to occur with anything starchy like rice and pasta.

A lower temperature should help to control a boil over as it will allow the water to cool somewhat and slow the boil.

I'd assume that, from your quoted text, that if you use less water you're still imparting the same amount of starch making a thicker solution. More water would dilute this and bring it closer to normal water. In my own experience, small amounts of water allow lots of bubbles to form but nothing really boils over, it just splatters a bit. But reducing temperature and tilting the lid to let some air in has helped me in the past.

As long as you are talking about a normal pot with or without a normal lid (i.e. not a pressure cooker) and you are reasonably close to sea level, you're right, boiling water is at 100°C. However, if you start to climb in altitude, that is no longer the case, at 300m, water boils at 99°C, at 600m, 98°C and so on. Wikipedia has a page with information about High altitude cooking that contains a reference table.