I accidentally plugged my USB mouse into my eSata port... it works?

I'm on a Thinkpad T510 and I accidentally plugged my Razor USB mouse into the eSata port not realizing my error because it has been working fine this whole time. Does this seem a little odd?

It sounds like you have a USB/eSATA combo port AKA eSATAp. Which enables you to use either the USB or the eSATA on that particular port.

Picture taken from: techarena's forum.

eSATAp is also known as Power over eSATA or eSATA/USB Combo. eSATAp port combines the strength of both eSATA (high speed) and USB (compatibility) into a single port. eSATAp devices are now capable of being self powered. On a desktop workstation, eSATAp port can supply 12 V to power up a 3.5" hard disk drive (HDD) or a 5.25" DVD-RW without needing separate power source as compared to eSATA and USB 2. On a notebook eSATAp port can supply 5 V to power up a 2.5" HDD/SSD as compared to eSATA. Many notebooks are now equipped with this combo port. A list of notebooks with this new port is available here. eSATAp can be implemented in all machines with a spare SATA port. These machines include PC notebooks, desktops, Apple Mac Pro, and Linux or Unix servers. This makes eSATAp an easy, economical, cross platform solution for external storage.

Serial ATA (Wikipedia).