I think the difference that the OP might be getting at is as follows.
The low-cost style bootstrapping would involve low to fully covered with savings personal living expenses for one or two people, and ramping up slowly, prioritizing profitability over growth.
It seems like (I don't know the whole story) in Flow's case, the decision was made to compete on an excellent consumer product. Those are hard to build. The fact that 10mil was wasted _probably_ indicates that they hired very good designers, programmers, etc at market rates to produce world-class work for a consumer product ("better than Asana"). Meaning, the typical bootstrapping to profitability ASAP was not a priority in this case.
However, if you sink that much money into a not very profitable business, after 12 years you might expect _something_ back. Maybe not the VC happy path 10x return, but after so much resources your expectations on return and growth rate etc etc are higher than a low-key bootstraper who might choose small-scale profitability over growth. So yes, it is self-funded, but he basically can't end up with a mom-and-pop style $200k/year niche business after he sunk so much money into it, so he de-facto pushed himself into "expected VC returns" territory.