The Polish translation for "naval" is "pępek" and not "popik". Being transferred from Polish to Yiddish the nasal sound "ę" was changed into "o" which is much more comfortable for Yiddish speakers. But maybe the borrowing from Russian пупок (poopok) is even more likely. Thanks for the interesting article.
Donald Trump: Israeli settlement construction in West Bank should 'keep going' (Haaretz)
from the article: Word of the day / Pupik