It's a performance error; the predicate should be nominative.

English pronoun cases don't divide up the same way Esperanto cases do (e.g., prepositions take the object case), but note that many English speakers say, "It is me" rather than "It is I". (I don't know Emile's first language.)

Also, leaving off the accusative ending is such a pitfall for most beginners at Esperanto that people sometimes overcorrect anything matching the pattern "nominative verb nominative" to "nominative verb accusative".

Edit: Corrected "pronouns take" to "prepositions take".