If you were to define it that narrowly any company that doesn't do its own accounting is not longer a "single person company". At that point I don't think you'd be left with many companies that make much revenue, so even though the code is open source that still counts as a single person company imo.

It's still a single person company (as in, the company with only one employee). The fact that more people contribute to the company's product doesn't change that.

As long as other open source contributors are not payed for their contributions, I would still qualify it as a single person company. It's just that the company's approach is a little bit different than the traditional one.

Not completely. However is commits or line changes mean anything, you can see at https://github.com/mperham/sidekiq/graphs/contributors that 1 person did approx 90%+ of the work on the code itself.

And why was I down voted? Really, I did not even express a strong opinion. I kind of expressed a doubt. This is really strange. I may not know something and I may have doubt. I believe a community like HN is a good place to express them and get corrected. I am shocked to see that this is not really welcomed here.