If I make a gas engine with 100% heat efficiency but only run it in my backyard, do the greenhouse gases not count because it's so efficient? Of course they do. The high efficiency of a data center is great, but that's not what the article laments. The problem it's calling out is the absurdly wasteful nature of why these farms will flourish: to power excessively animated programs to feign intelligence, vainly wasting power for what a simple program was already addressing.
It's the same story with lighting. LEDs seemed like a savior for energy consumption because they were so efficient. Sure they save energy overall (for now), but it prompted people to multiply the number of lights and total output by an order of magnitude simply because it's so cheap. This stems a secondary issue of further increasing light pollution and intrusion.
Greater efficiency doesn't make things right if it comes with an increase in use.