The notation p -> q refers to a conditional statement.
Conditionals are only false when the first part (p) is true while the second part (q) is false. In other words, the template true --> false ultimately leads to a false statement. Otherwise, the entire thing is true.
In our case, we have something that fits the "true -> false" template, so that's why p -> q is never true when p = true and q = false.
