Is this intended (not sure if I should Mantis it or not, I don't really understand its intended behavior)?
Its intended behavior is to throw a tantrum exo whenever you destroy something at least vaguely important to it, with the importance factoring into just how big said exo is. There's quite a few objects that trigger it and the description should be (not sure if it is) kind of open-ended about exactly what triggers it.
Not sure why the CSG caused such a big one for you, their TriggersExoOfThisBudgetTimesAIPOnDeathIfVengefulAI value is only 200. That's twice what it does when you kill a command station (and 4x a normal guard post), but I'm guessing you wouldn't be so surprised if the CSG only sent one 2x as big as what you've gotten used to thus far. Then again, AIP may have been significantly higher by the time you popped the CSG.