The (accented, as it must be here) πού is not only a questioning word. It can also emphasize a negation, as here, where you could translate «μα πού εκείνο» with something like "No way!" or "But it wouldn't" or something along those lines. In ΛΚΝ, we have:
πού [...] 2. ισοδυναμεί με ισχυρή...