This argument could have been made every time a new biological life form was found, and would have been correct every time; this does not mean it is impossible that in the future a biological life form that does not require water could be discovered.
This argument could have been made every time. A new biological life form was found every time. This argument would have been correct every time. This does not mean. A biological life form could be discovered. This was in the future. This biological life form does not require water. This is impossible.