Well, taken at face value, it is a bit of an oxymoron. To contribute is to be part of a group; by definition, a contributor can't be wholly independent, because they're adding to a corpus, not producing it by themselves.

It's been in use in engineering for decades now. My father was familiar with the term in his career, and he's pre-boomer.

"others like myself would rather kill themselves than work a 9-5 until they're 60". If its in a corporate hell-hole, I might at times feel like that too. However, not all 9-5s are equal :) Public sector such as govt or academia, or other non-profit, can be fulfilling and not soul-sucking. Or, at some point switch to something only slightly related to tech, such as teaching. People talk about "full fat" FIRE, but thats unrealistic and/or requires some years of miserable sacrifice for most people (being rich before you start, or getting randomly lucky with stocks, doesn't count IMHO). They also talk of "Barista FIRE" - i:e you can't totally retire but can work a supposedly low-stress job (personally, not convinced by it, baristas can still feel "oppressed" at work) . What about the middle road... which is, live frugally (which helps the planet too), over-pay mortgage and avoid other debts, with such an attitude hopefully most techies would by their 40s be able to work in a job with a moderate professional salary, perhaps arguably underpaid for what they do, but, if that's what necessary to be fulfilled at work and not feel like killing oneself, then so be it? ;)

And a lot of those people would not have been in a position to start their own companies--much less succeed at it.

Have a big trust fund? Sure. If it were from Day 1, depending on the circumstances, 9-5 would have been ehh. But not sure how directed I would have been absent strong parental direction.