Face down exiled cards are viewable by other players

[zoot4life]

My opponent played Gonti, Lord of Luxury and exiled a card from my library face down, but i was able to click the Moon/sun icon on the top left corner and flip the card over to see what it was. The cards exiled face should only be viewable to the player that exiled the cards.

406.3. Exiled cards are, by default, kept face up and may be examined by any player at any time. Cards “exiled face down” can’t be examined by any player except when instructions allow it. However, if a player is instructed to look at a card and then exile it face down, or once a player is allowed to look at a card exiled face down, that player may continue to look at that card until it leaves the exile zone or is part of a pile of cards that are shuffled, even if the instruction allowing the player to do so no longer applies.