That may well be, but the fact remains in modern business documents, it is an egregious error to type "pubic" when one means "public."
P.S. if anyone cares, here's the OED's etymology for "public":
< Anglo-Norman publik, pupplik, Anglo-Norman and Middle French public, publiq, publique, Middle French publice, publicque, puplique, French public, publique (adjective) of or relating to the people as a whole (first half of the 13th cent. in Old French), official (end of the 13th cent. or earlier in Anglo-Norman in instrument publik official document), authorized by, serving, or representing the community (end of the 13th cent. or earlier in Anglo-Norman in publique notaire public notary, persoine publique incumbent of a public office), generally known (first half of the 14th cent.), open or available to all members of the community generally (late 14th cent. in lieux publiques and places publiques public places), open to general observation or view, carried out without concealment (c1400), (noun) the community or its members collectively (1391; 1320 in Old French in en public in a public place, publicly, openly), state, nation (1559), audience, spectators collectively (1751) and their etymon classical Latin pblicus of or belonging to the people as a whole, common to all, universal, of or affecting everyone in the state, communal, authorized, provided, or maintained by the state, available to or enjoyed by all members of a community, in post-classical Latin also conspicuous, clear (4th cent.), of or relating to the nations generally, international (1541 in the passage translated in quot. 1548 at sense A. 2c), alteration (after pbes, in the senses ‘adult men’, ‘male population’: see PUBES n.) of poplicus < poplus (later populus) PEOPLE n. + -icus -IC suffix. With use as noun compare also classical Latin pblicum public interest, use as noun of neuter of pblicus. Compare also classical Latin rs pblica REPUBLIC n. Compare Old Occitan, Occitan public (c1170 as adjective and noun, the latter as publico, in sense ‘public treasury’), Catalan públic (13th cent. as adjective and noun; 1150 as adjective in form púlvego; compare post-classical Latin pulbichus, pulvichus, both 10th cent. in Catalan sources), Spanish público (late 12th cent. as adjective; 10th cent. as adjective in form pupligo; a1250 as noun), Portuguese público (late 13th cent. as adjective in form pulvego, early 18th cent. as noun), Italian pubblico (first half of the 13th cent. as adjective in form publico, first half of the 18th cent. as noun).