What about the sentence "Dzwonił palcami o szkło"? Wouldn't "palcami" be a direct object?
It looks to me like an adverbial complement describing an instrument.
But another reason for saying that -no / -to forms aren't true passives is that they can be used with intransitive verbs.
Jak tańczono przed wiekami.....
write the sentence in English and you will need a preposition (with his fingers) - I guess the 'direct object' in terms of Polish language needs to be in accusative (palcami is instrumental) or genetive (szukać, słuchać)
Examples from English are completely irrelevant for defining the internal categories of Polish.
I would provisionally say that direct objects in Polish can appear in up to four different cases.
accusative - mam samochód
genetive - szukam klucza
dative - ufam tobie
instrumental - pogardzę nim