I run such a company (https://coderpad.io/). One of the things you start to realize very quickly is that the term "lifestyle business" is often just a matter of convenience.
Put another way, a lifestyle business can be looked at as simply a good business patiently looking for its opportunity to go big. Or, a lifestyle business can be avowedly lifestyle. Businesses can change a lot over time.
It's also odd that you'd mention Buffer as being a candidate for a lifestyle company. They've taken about $4m in funding, which implies that they convinced all of their investors that they'd see a significant return on their money. That's not to say that they can't operate like a lifestyle business, but they are almost certainly looking to generate a very large return.
I'd love to hear/read about other such companies and founders. I imagine Buffer might be a real-world modern example.