The title of the HN post is a little bit confusing, at least for me. It's a company that was bootstrapped by an 18-year-old in 1997, which is now (13 years later) worth $300m according to its founder. The title here made me think it had been recently bootstrapped by somebody who is still a teenager and that it is now showing $300m in either revenue or profit.
When someone says $300 million dollar company, it doesn't mean a company with $300 million dollars of revenue or profit per year. Generally, it means the valuation (based on any number of measures, ie. acquisition price, last traded price x number of shares outstanding, founders pulling a figure out of thin air, etc.) of the company, so revenue can be anywhere from $0 to $300+ million (generally around single-digit multiples), and profit can even be negative.
The traditional meaning of an $x billion company is by revenues. Using it to mean valuation is quite new, and limited to startup/Silicon Valley people.
In general, Wall St tends to use this nomenclature (i.e., $X billion dollar company) when referencing revenues. For instance, Procter & Gamble is referred to as an "$80 billion dollar company" - which speaks to revenue, not market cap.
This gets murky with private firms, since revenue isn't typically shared, and even more so with startups where so much of the value is based on future, projected earnings.
In general, though, I'd say the nomenclature more commonly refers to revenues and not 'valuation'.
