My guess is that they counted each line of code made by an engineer using AI coding tools.
Besides, even google employees write a lot of boilerplate, especially android IIRC, not to mention simple but essential code, so AI can prevent carpal tunnel for the junior devs working on that.
Roughly only one quarter (assuming they are outputting similar amounts of code as non AI using engineers) of engineers actually using AI regularly for coding is a statistic that is actually believable to me based on my own experience. A lot of small teams have their "AI guy" who has drunk the kool aid, but it's not as widespread as HackerNews would make you think.
Besides, even google employees write a lot of boilerplate, especially android IIRC, not to mention simple but essential code, so AI can prevent carpal tunnel for the junior devs working on that.