Her reply is interesting. She doesn't technically say that she ate a pork burrito, only that there might of been some cross contamination. Also, if she did eat a pork burrito, how much/many did she eat, and could it get her into the prohibited range? I'm hearing that she was a decent amount over acceptable levels.
This supposed Mexican food truck is the boogeyman here, they want you to think of dirty 3rd worlders, cooking up pigs from some strange dirty farm, or perhaps poached / hunted from somewhere. I suppose something like that last part could happen, but it doesn't make much sense. Good, clean pork is dirt cheap here in the US, and also almost all commercial pork is castrated early on to help cut down on male hormones favoring the meat ("boar taint"). We also don't use nandrolone as a growth drug in farming.
This is one of those stories just plausible enough to make people shrug and perhaps dismiss the results. I wouldn't be surprised if a lot of guys keep the tainted pork excuse in their back pocket for just this type of thing.
Like Brian, I'm thinking someone gave her something mislabeled, or she decided to go off program, and added it in herself.