I'm not really sure which party is truly in the wrong here but following the reveal that Nintendo and Square Enix were holding their E3 2015 events at the same time, Square Enix decided to back down.

Square Enix originally scheduled their event for 9AM on June 16, the time Nintendo typically held their E3 events. Nintendo then comes along and schedules their event for the same time. Today, Square Enix decided to reschedule their event for 10AM on the same day. I know it's "tradition" for Nintendo to hold their E3 event at that time and that day each year, but it's still kind of crummy that tradition overrides a media event that has been scheduled for over a month already.