TheWoWDBMore than likely this is just the NPC they generated to say Sargeras' voice lines in the quest In My Father's House, so that it can show up in the chat log as "Sargeras says:" etc. And of course the Sounds tab on NPCs has him as an infernal, the usual placeholder for NPCs who aren't going to physically appear to the player.
Elite
Sargeras
The highest voted Wowhead comments for this page. They are community notes, not TheWoWDB comments.
Could it be?
Aw #$@& it's big bad himself
Details
This roster comes from the current game client's data files, so it is not a complete list of every NPC in the game - older world NPCs that are no longer in the modern client are absent.
Community notes from Wowhead · 5 comments
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Level and Map Tracking
The game data tunes Sargeras for levels 10 to 45, Legion content.