Why would you call colocation "building your own data center"? You could call it "colocation" or "renting space in a data center". What are you building? You're racking. Can you say what you mean?
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Cloudflare has also historically used “datacenter” to refer to their rack deployments.
All that said, for the purpose of the blog post, “building your own datacenter” is misleading.
I think you're conflating things.
Those hypothetical hyperscalers can advertise their availability zones and deployment regions, but they do not claim they built the data centers. They provide a service, but they do not make broad claims on how they built infrastructure.