Your ticket has received the following response:
<Greetings,
Thank you for contacting us today.
I understand you’re concerned about the functionality of the Infernal summon, mainly that it was changed from how it was back around vanilla times vs how it is currently in Wow classic.
Contacting a dev isn’t something you can really do via this channel, the best way to reach them is honestly twitter, they often keep an eye on things there and in the forums, but I cannot promise they will be able to reply, still, give it a shot and hope for the best. I did however look into the bug report we submitted and good news, it is actually getting eyes on it as I send this, they’ve done some testing and should hopefully update the not a bug list with some info.
Now regarding the Infernal itself, I dug into it and here is what I found. Going back to Wowpedia, they do a good job of tracking patch changes: (redacted link) there is a call-out for 1.5.0 where it does mention that after the enslave runs out, it will target the summoner, this is intended behaviour.
The aura you’re looking for is “Demonic Immolation” you can actually go here for the info: (redacted link) So they do have the aura, but it is activated on damage taken. Since on breaking enslave it targets the warlock, in theory if you attack it, and it pulses it can hit and aggro guards and others.
Here is an example I found online of this, (redacted link) actually found it in a similar thread to yours: (redacted link) . However that video essentially confirms how it is intended to work, minus one small caveat I will explain further down.
Actually, I believe the behaviour also matches what you see in the video you shared from what appears to be a private server. Though I am not sure how accurate it is since after all private servers weren’t fully accurate either. But note at the end when the night elf is tanking it, the aoe only hits folks who aggroed by helping the nelf or attacking the Infernal.
Now back to the video I shared, notice the Infernal only aggroes the guards (because of the aoe pulse), pvp players (green name not blue) and players who attack it or in some way generate threat with it (healing the warlock). It ignores players who ignore it, and then eventually returns to the summoned spot and moves around a bit and then eventually leaves after about 5 to 10 secs with no target. This is why the warlock in the video soulstones himself, revives and then doesn’t attack the Infernal again, to avoid being killed. It’s combat behaviour is accurate to Vanilla, it only attacks pvp targets, guards, pvp flagged players, and like any creature it attacks anything that generates threat on it, either by attacking it, or healing something that threatened it.
Turns out that is the only different right now in Wow Classic, and the caveat I mentioned, is when it runs out of hostile targets to attack, it doesn’t run back to its spawn then patrol around then despawn. It runs back but then just stands still at the spawn location then despawns, same duration as before too, 5 to 10 seconds. That is the only difference now versus back in actual vanilla wow, and it is being looked into to see if we can make him walk around a bit again. Reading over that post I found the video in the player Jespari seems to realize this as well and tries to explain it to everyone.
Hopefully this clarifies the situation and how it seems to be working as intended minus the patrolling.
Thank you for contacting us about this and let me know if you need a hand with anything else. 
For any random questions, don’t hesitate to ask or check out the main site (redacted link)
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Regards,
Blizzard Support