I think it just means Slyveon is the first unveiled and marketed. It'd be weird to refer to it in any other way.
Really, Xerneas & Yyveltal are just kind of...there, at this point. Hopefully July gives us their type and purposes and such.
At this point.... I'd have to agree with you. As you've pointed out earlier they should AT LEAST give us the name for Mewtwo's new form on the 11th, it has been long overdue.