Linguists indeed think that this similarity is an accident. The Hungarian fiú s an old Finno-Ugric word, not a Romanian loanword. In Finnish it is "poika", and in Komi (spoken in Northern Russia) it is "pi". The Finno-Ugric p has systematically changed into f in Hungarian. Other examples between Hungarian and Finnish: fej = pää (head), fészek = pesä (nest), felett = päällä (on / above), felhő = pilvi (cloud), fecske = pääsky (swallow). The Romanian fiú comes from the Latin filius, as MrtonPolgr says. There can be similar words in geographically close but unrelated languages, and still these words are of different origin.