If the designer wants to make text big, they should first set somewhere a specific value for its size, not go on to "you like your text this way? fuck you, i'll make it bigger than that!". There was no "px" or "pt" size setting anywhere higher in the DOM, so that's effectively what the author was saying to the readers.

> If a user doesn't, they can easily make it smaller.

The user already set their text preferences in browser settings. It's the designer that decided that they will make every user, who made that choice at some point, miserable.