There are posters on both sides that have made claims of authority. Pick the interpretation that suits your table/players best. Probably best to refrain from making statements about the other side "playing incorrectly" though.
The Parsimony argument is specious. You could as easily say that one side requires only the assumption that spells do what is presented in the spell effect and nothing more; while the other requires multiple assumptions regarding the similarity between magical fire and mundane fire, and the similarity between IG fire and IRL fire, etc.
It deals fire damage?
Anecdotal evidence and real world physics are simply not informative to understanding the game mechanics (see falling), doubly so when the game mechanic under discussion is a magic spell.