Ehh… On the one hand, I can see where you’re coming from, but the jam is clearly focused on one thing and one thing only: positive representations of polyamory. All the rules exist for that purpose - and, importantly, they’re written for people who don’t necessarily know what polyamory is or what a positive portrayal might look like.
For example, the trope of a “love triangle” isn’t just two characters in love with the same character, it’s generally also associated with jealousy and competition between the two love interests, with the idea that one of the love interests will “win” and get the girl or boy. That’s not polyamory, but people unfamiliar with the concept might mistake it as such, so that’s why the rules call it out.
I can’t speak for the jam hosts, but I imagine a situation that starts out as a typical love triangle but ends with the connecting character choosing both, or with the three of them falling in love with each other, would be just fine. (This kind of situation is even one of the examples provided in the description of the jam.)