If that were the case then Stargate is already a thing because OpenAI must have a data center somewhere already.
And yes, the plan was for it to be 170km, since it was announced.
From there, The Line =/= Neom. That said, 170km is still the plan for The Line – the first segment was supposed to be 5km by 2030, now it is 2.5km by 2030. And again, them not building as much as they said does not mean it is cheaper (cost is what we're discussing, after all). If anything it means they are already over budget.
Stargate is a new company, so OpenAI (a different company) having data centers does not seem relevant. Also, I do not think OpenAI actually does own any data centers – for the most part they've been using Azure infra AFAIK. But I did not claim that Stargate was imaginary, so I am unsure how this is a relevant point for you to make.