Tbf, it sounds like neither side did a stellar job here.

Poland not reacting "for several hours" makes it sound almost deliberate.
Then again, I wonder how German police "informed" Poland for there to be no reaction. Did they fax?
If they think the situation requires an immediate reply, why not call them? Surely a dedicated border patrol unit would have a contact number.
Also, despite Schengen I don't think police can just cross the border to another state unless in pursuit of some fleeing criminal.
And just dumping these people in some random location without any involvement of local authorities doesn't seem like proper protocol.