As an Athenian he was an outsider to the Spartans the direct translation does make sense, but does anyone know if this name was inherited or posthumous? For someone who spent much of his life being an outsider to whoever he was around his name feels a little too accurate
As usual w/ classical Greek sources I can find nothing
(this is the Anabasis Xenophon just to be clear)
Xenophon is a perfectly ordinary name in Greek. Among the many holders of the name include an Athenian στρατηγός in 430, the famous historian/philosopher, a comic poet roughly contemporary with said writer, the geographer Xenophon of Lampsacus, the prose writer Xenophon of Ephesus, sculptors, physicians, etc. The name has nothing to do with any foreign-ness (I would suggest taking the meaning of ξένος not to be foreigner but to be host, which is possible, though I don't know if anyone's ever bothered to parse the name), nor do I know of any attestation for a Greek changing his name or receiving a new name later in life other than the Macedonian kings and those who received Roman citizenship. Weirder is Xenophon's father and son, both named Γρύλλος, literally the performer of some kind of weird dance--to my knowledge these two individuals are the only ones known to have the name