Yes, you get a bit into semantics here but my view of it is that blossom is the procol that by its nature allows easy formation of a CDN.
It's unlike legacy CDNs (like CloudFlare) where you need to trust one large party.
Caching and saving in blossom are the same, really. You can keep all videos/images you watch on nostr for 2 weeks and then drop them. In the meantime you can allow friends/family to load the files from your blossom instead of the original poster which might be on the other side of the world...