What was wrong with this animal?

Yesterday me and my friends came across an armadillo with a weird yellow goo or substance come from it's back and it was all over its shell there were flies sitting in the liquid it was disgusting on of my friends said it might be some kind of infection we tried to call animal control but they never my friend then stated she wanted to kill it with a rock so it didn't infect other animals luckily I was able to prevent that but I was wondering what was that on the little guy and was he even infected with anything in the first place