Having an AS does not make you an ISP. It just means you have a public AS, which you can use to peer with providers on the Internet, if you have an agreement to peer.
Correct. In fact many, many companies have ASNs. Little companies all the way up to large ones. The key difference for an ISP is they allow you to route traffic through them. Almost every company that has an ASN blocks traffic from being routed through them, assuming they know how to configure that and that they have different peering points. Valve most certainly does not allow you to route through their network, they already have enough traffic just doing their own CDN stuff.
Having an AS does not make you an ISP. It just means you have a public AS, which you can use to peer with providers on the Internet, if you have an agreement to peer.
Correct. In fact many, many companies have ASNs. Little companies all the way up to large ones. The key difference for an ISP is they allow you to route traffic through them. Almost every company that has an ASN blocks traffic from being routed through them, assuming they know how to configure that and that they have different peering points. Valve most certainly does not allow you to route through their network, they already have enough traffic just doing their own CDN stuff.