Recent Android on T-mobile US uses IPv6-only transport. T-mobile's DNS servers are only asked by these devices to translate hostnames to IPv6 addresses. If they can't find an IPv6 address, they will look up the IPv4 address for a hostname, and pack it into the bottom 32 bits of an IPv6 address that routes to a IPv6-to-IPv4 NAT device at T-Mobile.

This is called DNS64/NAT64 and has some small performance penalty. Making content directly accessible by IPv6 removes the penalty.