Mathematically that would work out to a lot less than 8 layers of management.

I wonder if they have 5-10 employees per manager at the bottom of the org chart, but a lot of middle managers and manager-like titles mixed through the middle.

At 8 layers of management (so 9 layers total, with the bottom rung being non-management), 3 reports per manager comes out to 6561 employers on the bottom rung. At 5 reports each, that 8 layers would give you over 300k at the bottom, an 10 each would give you 100m at the bottom.

That's a really crazy number of employees considering they have one product that barely seems to change and is at best on par with similar products created by comparatively miniscule teams (Phabricator, Forgejo).