How do you know HE has these powers? How do you know he's not using some sort of technology? How do you know he's not being controlled by some other being? How do you know he wasn't given those powers by his "employers"?
Just because he has unusual powers doesn't mean he's NOT from Earth...
First, just because Antlion Husbandry was their Ancestral practices doesn't mean they'll get a long.
Second, the Extract helps them do what they did with Alyx, it has special healing properties and such.
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So yeah, clearly the Antlion's are from the same planet/universe as the Vorts...
It's presumably filled with flammable gases, as... well... it can release fire from it's claws, which, in effect with firepower, can make it explode which is why it has that death sequence.
Also like SamuraiKenji said, it's a '95 game, what do you expect? Some big over dramatic graphical death...