Avatars and Shrines can be hit by certain abilities.

Reproduction steps:
1. Deploy any champion with "X attack" 2-4 RNG ability chain, an example of that would be Magical Attack.
2. Walk up to a shrine or an avatar.
3. Use the ability.
4. The ability will properly fire off instead of stating you're trying to attack an invalid target.

@Sokolov

 

If it's an Avatar, it's a bug. However, shrines can be hit with non-basic attacks.