It could be an accident - Hermione hits a chandelier with a cutting cures, etc. It's a fight, things like that happen.

Agree. Not sure how such a mutual trap would expose their manipulators either.

Whoever's manipulating them is probably not anticipating a team up. (And if they are, they're beyond the two's ability to deal with anyway, so no point in worrying about that option.) So, Hermione apparently gets taken out of the picture, while Draco is free to investigate what's going on with a manipulator who's moving ahead with his plan.

... Okay, so that was kind of nonsensical since I was deciding what my opinion was while I wrote it. Let's try this again:

Hermione and Draco meet, and actually talk it out. They decide to work together against their mysterious puppetmaster by playing along with the plot, as opposed to completely derailing it and then not knowing who was behind it.