Yeah, from what I've read which includes what you cite here, we should not expect every new port to utilize Metal because a lot of work needs to be done for it to offer all the features needed.
I imagine it'll be great when possible and hopefully Apple will continue to add needed enhancements to it but for now I actually will be assuming something is not going to be using Metal unless an announcement specifies otherwise.
On another note, since the system requirements for the game do not require El Capitain one can derive from that it isn't a port done with the Metal API.
