I suppose a question..eSATA uses an eSATA connection. I don't know why that would have caused a problem for a keyboard.
Did your actually connect an external drive to a USB port under the conditions you mentioned? Are you thinking you may have broken the USB connectors? But, I suppose either situation might have messed up a particular voltage output on the motherboard.
I would think external devices are designed in such a way that forgetting the power supply for it would not break the motherboard. Plus, eSATA does not even draw power from the connection.