i dont know if its true or not, i just dont think one should go about demanding a source of every maaseh one hears.
certainly one should learn Halachah from a sefer and not from a maaseh. (although middos and derech eretz are a different story, of course)
i didnt realize that that was NOT a Halachah. i thought the maaseh was just an illustration of the Halachah. i assumed it was a Halachah because ive heard it said many times (as a Halachah, not just a maaseh) (just said stam not authoritatively)
thank you for pointing that out