It was an editorial mistake, not a grammatical error. The project was announced in June, 2011 but the wording implied that it happened last June. Had the writer actually meant last June, the clearer way of saying it would have been simply, "the project was announced in June." The word "back" in this context would be redundant (not needed to express the meaning of the sentence).
Thanks for asking. I'm always impressed when a non-native English speaker shows an interest in correct English grammar, when so many native English speakers no longer seem to care.