“Ale” and “beer” have not always been synonymous. Used to be ale didn’t have hops, for one thing.

Zythophile (a favorite read of mine) offers up a lengthy article on when the two terms merged. It’s not as simple as many think.

Why weren’t stout and porter called ales? This is a reflection, 200 years on, of the origin of porter (and brown stout) in the brown beers made by the beer brewers of London, rivals of the ale brewers for 500 years, ever since immigrants from the Low Countries began brewing in England with hops.

Zythophile: The long battle between ale and beer