They're allowed to do that if they want to. Most find there's no practical reason to ensure the addresses are related. It wouldn't help them support v6 faster.
Do they own such an address, as in, a packet sent by someone on another ISP to that address will actually reach my ISP's router over v6? Not talking about translations that use v4. If they do, I've never seen them actually give it to me.
Yes, they can just put your 32-bit IPv4 address after their 32-bit prefix, and that gives you a /64 as is standard. If they want to. But what's the advantage?
Traffic to 2002:70.94.201.31/48 is tunnelled via 70.94.201.31 with-in an IPv4 packet (encapsulation):
* https://en.wikipedia.org/wiki/6to4