I think it's entirely reasonable to ask questions when something is not clear or requires explaining.
The main point I'm always seeking to put across is that it's unusual for the school case to fail at stage 1, and your energies are therefore best focused on stage 2 which is where most cases are won or lost.
In my view, for a school to lose stage 1, the case would probably have to be incompetently presented, or alternatively the school is eager to accept extra pupils! (The latter situation occasionally arises when the LA is the admission authority and is determined to resist, but a school representative states under questioning that additional numbers would not cause any problem.)
You have every right to ask for clarification, and might even dent the school case a bit in the process. Parents can sometimes get very angry at a group hearing, and it's always best, I suggest, to ask questions in a very reasonable manner, rather than launching into a full-frontal assault.
Stage 1 is also known as the "factual stage" - the panel is there to establish the facts, and cannot be swayed by the strength of feeling.
Hope this helps