I read in this page that shopify's CDN is Fastly.
But I also see in the HTTP headers that the CDN is Cloudflare.
Which one is Shopify's Official CDN?
It's strange that there is no documentation about the change if it was made.
The CDN provider is somewhat irrelevant as they'll use what makes sense for best coverage and speed in each region. This could change and augment over time.
That link isn't wrong, Fastly is one of the CDNs that Shopify uses.
For sheer curiosity, why does it matter which they use? Does it change what you're building somehow?