Handles have to sound like names, not neccessarily human names. Also even if Teyacapan Quetzalxochitl was unacceptable that does not mean further unacceptable names should be accepted, that would be stupid.
"Thunder" and "Neutron" are both actual words. "Teyacapan" and "Quetzalxochitl" are not and are both plausible names (Aztec, even). These rules are clear on the Character Creation rules that your rejection mail links to, so please read them before requesting a handle. Your name will be the name of your character, not a nickname for your account, so select a name accordingly.