Patient X is diagnosed with a certain disorder and his doctor starts treatment. Upon Patient X's death, it is discovered he actually had a different disorder. This doctor demonstrated:

a) reliability and validity
b) neither reliability and validity
c) validity, not reliability
d) reliability, not validity

it was a recent test question i had on an exam. Can't stop thinking about it. I picked B. Any ideas?
I have -pathetic- grasp of stats, but it seems to me...

He was reliable (diagnosed a problem and correctly administered treatment)... but not valid (the diagnosis itself being incorrect, it was virtually guaranteed to fail)

But if those words mean anything different in stats......