The article claims there were "several hundred" cheap seats available, which I assume is correct, as vague as the term 'several hundred' may be.
The fact that they go on to then say that "The marketing method, pioneered by Ryanair, has been criticised in the New York Times, which said the airline "offers a kind of bare-bones intercontinental travel that American travellers may be unused to"."
Americans are more than used to "bare bones" air travel. Their airlines practically invented this. These EDI routes are barely 500 miles longer, or less than 90 minutes of additional travel, when compared to some of the longer coast-coast domestic service which all come under the bare bones flights where refreshments, food and bags are all chargeable extras.