>>42508286This was intentional. You'll notice a lot of the G-Maxes have this as a gimmick, examples:
Appletun/Flapple: You do not know which of the two it is until the Raid begins. (exception: you know if you're the one starting the raid as it will be based on your version)
Alcremie: G-Max Alcremie always looks the same regardless of what color the Alcremie actually is. You do not know what color your Alcremie will be until after you catch it.
Toxtricity: G-Max Toxtricity has elements of both Toxtricity forms. You will not know which form yours actually is until after you catch it.
It's designed to keep you playing raid battles even after you've caught everything, I guess.