There are in fact three varities of tetnus vaccine available in the US. (Gracey worked at a lab through Grad school)

What came out of your arm is basically "waste material" that was part of the suspension for for tetnus antibody. Dont' worry about it. Some people absorb it, some dont. It does give away what vaccine was used however. . .a very CHEAP one. But I'm sure you got charged $100 + for it. Medical care in this country sucks.