I've heard some similar stories in my family as well, but wanted to add that there were other reasons as well why siblings might have wound up with different surnames.

Surname adoption in Eastern Europe tended to happen between 1808 and 1826 (i.e. after the Napoleonic Wars), and generally speaking people didn't have surnames prior. There were various taxation policies around that time that may have made it advantageous for two siblings living in separate homes to adopt different names. I don't recall my source for this, or the details, unfortunately. Might have been an article on Avotaynu.