It was presumptuous of him to make a remark in the assembly.

Ridiculous : deserving or inviting derision or mockery; absurd.
Unthoughtful : showing little or no consideration for the needs of other people; thoughtless.
Overconfident : excessively confident.
Ambiguous : open to more than one interpretation; not having one obvious meaning.
Presumptuous : (of a person or their behaviour) failing to observe the limits of what is permitted or appropriate.

Synonym of Presumptuous is Overconfident