patterns of inference - medical diagnosis - lung disease

[MikeTam1021]

In patterns of inference, on the example Medical Diagnosis halfway down the page this is stated:

"To illustrate, observe how the probabilities of cold and lungDisease change when we observe cough is true:"

followed by:

"Both cold and lung disease are now far more likely that their baseline probability: the probability of having a cold increases from 2% to around 50%; the probability of having lung disease also increases from 1 in a 1000 to around 50%."

This seemed wrong to me immediately, considering the code is:

var cough = (cold && flip(0.5)) || (lungDisease && flip(0.5)) || flip(0.001);

lung disease and cold should have about the same prior probability.

the actual code looks like this:

var smokes = flip(.2);
var lungDisease = flip(0.001) || (smokes && flip(0.1));
var cold = flip(0.02);

which means lung disease is 2.1% given you know nothing about the patient or, expressed similarly, 21 in 1000 to around 50%