I haven't looked at the code, but I'm guessing average is taking the ping time from the last server update. The server updates every 100ms (10 times per second).
That means if you have 0 latency and a fast computer and send a packet to the server on the same frame it's doing its update, you could get a 0 ping. If you send an update just after the server did an update, it won't respond until the next update, meaning your ping would be close to 100ms. On average, this would be close to 50ms, best case.
I suppose this is accurate, but it's not the numbers we're typically used to. It will, in practice, take an additional 0-100ms for the server to respond to your input (ex: the time between clicking the mouse button and when a paintball fires). The average latency is the normal ping + 50ms.