If you are selling in the US, and an account with a primary address overseas buys your item and uses a US shipping address, you are likely shipping to a package forwarder. These services are common because many people and businesses in the US only ship to the US.

I have my eBay account set this way, and I still get bids from overseas accounts -- I always Google the shipping address, 100% of the time it has been a package forwarder.