You mean a hot surface like a set of hot brakes just after landing...
Basically what I'm saying the Fire Crews were there, looking at the situation, knowing what the possible scenarios are (is this fluid oil, is it fuel) and have correctly assessed that the fluid dripping onto the hot brakes and vaporising represents a significant fire risk and have given their advice. They were there, they had all the facts and trying to armchair quarterback a decision made by someone who is an expert in their field (a field which, I would postulate, you know little [namely firefighting and fire development]) is not helpful when a decision was made in the interests of securing immediate safety for the passengers.