In former times some end blown recorders (self made) were played by the cildren of my home county till the end of 19th century/beginning of the 20 century.
They were made from willow branches and produced singing a special song: Saft, Saft, seire = sap, sap, (untranslatable). During this song the bark was beaten with a wooden stick till it loosened and the bark could be drawn off. Then the mouthpiece was cut off the wooden soul and inserted again, and the slit and holes were cut into the bark.
I never did it myself, but it must have worked - how else could the song have survived so long?
The recorder seems to be the older version than the traverse flute.
The three hole pipe was not uncommon, but always played with a little drum hanging from the left wrist, and it needed a lot of training.
The idea of a time traveller introducing a penny whistle should fit very well with Malcolm's proposition of a rustic flute.