What is the meaning of "birds of a different feather" in this context?

Question

Context: Germans captured Carnaby while he traveling to Russia. Kramer and Rosemeyer are trying to get information from him. Germans captured some rescuers (British Agents) who are trying to save Carnaby from them. Kramer gave a drink to Carnaby but Carnaby not consuming it, so he said this words to Carnaby.

You are not drinking, general. That's understandable when your rescuers turn out to be, well, birds of a different feather.

Does it means Rescuers are Germans but disguised as British agents?

Answer 1

Assuming your excerpt is from the 1968 film Where Eagles Dare, Carnaby is a captured American general awaiting rescue from Allied forces. When the rescuers arrive at the castle, however, they identify themselves as German double agents.

The quote is a reference to an English proverb— birds of a feather flock together, meaning that similar people tend to associate much as birds of the same kind form flocks. According to The Phrase Finder, it dates to at least the mid-16th century, when William Turner wrote

Byrdes of on kynde and color flok and flye allwayes together

in The Rescuing of Romish Fox, an anti-Catholic satire.

It is common enough the birds of a feather on its own is understood to refer to people of the same kind. Carnaby's rescuers are birds of a different feather— Germans— with whom he would not wish to "flock," as opposed to the British-American force he might have been expecting.