55k is not that much imo. ~50k people are born everyday in China and if we assume that the same number reach an age where they need a bike everyday the number seems quite reasonable. Maybe even a bit low taking the export market into account.
edited: Also lots of great durable bikes are made in China.
Yes you're right it doesn't seem astronomical, though I'm sure the global number is higher. But, China's population is now shrinking I believe, and I don't think bikes are grave goods.
edited: Also lots of great durable bikes are made in China.