"So, on the basis of what I said above, you could call an ale a beer, but you might not call any beer an ale. The term 'beer' is generic, as I said, and could conceiveably be used for any type of beer including lager, stout, porter, mild, bitter, or any other kind of ale."

You COULD call any ale OR lager a beer, but you might not call any beer an ale or a lager.

Beer, ale and lager are all generic terms - ale and lager are types of beer and there are many types of ales and lagers.