This is a complete hypercorrection. English grammar is NOT comparable to Latin grammar, although it is somewhat comparable to French (where, surprise surprise, the rule is "C'est moi" -- "It's me.")

To put it more technically, the subject complement doesn't fall into the "nominative case", which in English exists only vestigially in singular subjects, but rather the "disjunctive". The disjunctive is used for emphasis or when, for whatever reason, the subject is not the explicit actor of the verb (which in this case is "This is...").

Spoken English similarly mirrors standard French with the use of disjunctive pronouns in compound subjects, such as the commonly heard "Me and him are going to the shops". In this case, disjunctive pronouns are again preferred because the explicit verb-subject agreement has been broken (you cannot say "he are going" -- what you are actually saying is "Me and him, (we) are going...").