Despite their recent adventures, running into a dragon was usually a horrible thing. Dragons were powerful, typically, so they could choose to be really violent if they wanted to! In this case, a dragon floating above lava was less than friendly, the team was in big trouble.
They only had two options here as far as anyone was concerned. They could either run away and hope for the best, or they could attack the yellow dragon directly!
In this case, the first option was ruled out in three seconds, without giving much thought to it as an option. The team weren't keen on running away, and odds were that they couldn't outrun a dragon anyway, no.