From a calculation point of view, this may be true, but it is only half the truth.
While there is nothing wrong with your explanation and all are valid points, context is key, when the statement you quote is read within its context, it provides the complete truth, not just half.
...however, I think it's important to inform whoever is voting that the probability of finding is the same for 24 hours with 50ph and 12 hours with 100ph (with everything else being equal)...
With "everything being equal" includes, no difficulty change, no aliens' invasion, and you mine into the current epoch, your chances of hitting a block with 50ph for 24 hours are exactly the same as 100ph and 12 hours.