They could be coming either way. Both the Post Office and UPS are global, as are Fed Ex. My guess is the person who shipped them probably used the easiest method and went to the local post office. Every time I've ordered anything from Japan (always from companies like CD Japan), it's shipped via Global Express Mail (GEM). Cool part about GEM (along with "normal" express mail) is that it only takes maybe 4-5 days to arrive AND they deliver on Sundays AND holidays (Christmas, Thanksgiving and New Years included).
So if you're lucky, it was Global Express Mail. GEM has to be signed for though... so maybe it didn't go that route?