He did work toward it by saving and living frugally.
As someone who has successfully FIREd, I would disagree. If you are fortunate to be in a successful tech career and have a like-minded spouse, you don't need to do anything extreme to be able to FIRE. We only own one home that is comfortable but not impressive; we take care of our cars and drive them 10+ years; we leaned into hobbies that are cheap or money-saving (cooking, gardening, hiking, biking) and didn't get into owning boats or taking trips with first-class airfare and all-inclusive resorts.
I would say we "live humbly" and therefore had savings that covered expenses well before the age of 65. Part of our motivation was early retirement, but you can be doing the same thing without intent to retire early.
If it gets you to the point that you could retire early, then you were following a FIRE strategy, even if you weren't doing it with that goal in mind.