*edit According to uberbills http://casascius.uberbills.com/?address=1DtmMLhBQoiwUtdg18h7AFA4m57Vte3EGi, this is a june 2012 coin.
I'd assume its the acid in the ketchup, mild enough that its not going to corrode the metal more, but strong enough that it will actually work, but thats just my guess, I'm not cleaning it.
The 2011 Casascius coins were made, and they were funded at time of sale. If he didn't sell them until 2012 then they weren't funded until 2012.