However, Scald Emboar has never really had a good explanation.
Super late response to the Scald Emboar discussion, but it just occured to me that Emboar, as confirmed by Gen 5 interviews, has a lot of distinct Chinese inspiration.
The Unova starters were inspired design wise by three "empires", so to speak, one being France (Serperior), one being China (Emboar), and one being Japan (Samurott).
This works with Emboar getting Scald because people in China love boiled water and drink their water hot, and they have done so since ancient times.
Scald's Japanese name is literally ねっとう , which is "Boiling Water". Which is literally the term for what Chinese people drink: boiled water.
So it's likely a sort of figurative shout out to the culture Emboar was designed around in a sense. With Emboar having a distinctly Chinese inspiration, it's likely a shout out to that aspect of China and it being a fire type means the Water it can use is extra hot. Much like how people in China drink hot water as a cultural tradition.