So, if I understand correctly, my posterior probability is a distribution over the (p, q) space; and presumably, the particular data I've got becomes more likely as p approaches 2/7 and q approaches 0. So if I had, say, a uniform prior, or a prior that was uniform in the lower-left corner where both p and q are small, then I'd move towards zero q and nonzero p, or in other words "The line causes the crash". That seems to make sense.