Hello there,
this is about a bug on twitch.tv, not the meta-plays twitch feature. Some twitch streamers have their game still set to "Age of Mythology: The Titans" or something like that. However since the AoM games on twitch got merged, those game directories do not exist anymore.
BUG:
Below the stream the game shows "Age of Mythology", but if you click on it to see the twitch game browser for Age of Mythology, the streamer from which you came there does not show up as an online Age of Mythology player. Thus he may be harder to find for viewers.
FIX:
Change the game maybe to something else and then back to Age of Mythology. Maybe changing it directly to Age of Mythology works too.
Changing the game is possible in the twitch dashboard.