Most likely these are anycast hosted in multiple locations. From the west coast of the US, I can get responses from c,g, and h in under 60 ms, which means I'm hitting a replica within North America. I get a response in about 165 ms consistently from a, so that may well be hosted exclusively in a single location.

Also,

    host -t TXT -c CH id.server X.nic.es 

Indicates Calgary, Seattle, and "us" for c,g and h. a didn't seem to provide any useful information in the CHAOS records that I tried.

Doesn't look like it: https://atlas.ripe.net/dnsmon/group/es.