First of all, there is a neutral ad around every Centipaar Swarmer. They shouldn't be there, the Swarmer should summon them (as hostile).
You can't flee from the neutral ads (as the reporter says).
The swarmer summons only one additional ad, instead of summoning a lot with a pretty slow time interval. This additional ad is hostile as intended.
The additional hostile ad is refilling his hp to 100% pretty fast. This means, if you are not strong enough, you can't kill it, because - seems like - the Swarmer is "renewing" his ad (if that makes sense).
According to wowhead, these summoned ads should have way less HP (little enough to be killed by a magma totem, for example). The ads on AA (to be correct, the only ad) have ~1500 hp.
If you kill the Swarmer, the ads shouldn't despawn. On AA the spawned hostile ad despawns, while the neutral remains.
Centipaar Swarmer summons the Silithid Swarm. If you try to flee from the fight the Silithid Swarm will follow you until it is killed or you die.
In the image, the Silithid Swarm is following me for miles.