In the Talmud in Nazir you have a case around page 32 or so where two people see someone coming. One thinks it is George and the other says it is Simon. The one that said it is George says "if it is Simon I will be a nazirite." The one that says it is Simon says "if it is George I will be  a Nazirite" If it is Simon the first one who thought it is George is a nazirite.

Why is this any different from nidrei zeruzim of other kinds of vow where one really does not intend the vow to actually become obligated?