Hmm... ~wishes there were an amused, raised eyebrow emoticon to put here~
Perhaps meeting Bosch, and the presumably completely different reaction of the majority of the Iceni's crew, is what made them realize that Terrans must not be of a hive mind?
I still tend to default to the idea that unless the Shivans have been around for a ridiculously long time(and witnessed the countless tides of civilizations rise, war and fall, and decided they had to do something about it), they're more likely acting out of self(-species/collective) preservation, than any kind of 'external' philosophical purpose(though it's hard to know for sure; obviously, we know they have very advanced technology and understanding of subspace, so there's no reason to think they can't have developed higher philosophical leanings).
The 'hive-mind as their only understanding in relation to others' context definitely nicely explains the seeming disproportionate retribution aspect of the Shivans. Fits nicely into my thinking that the GTI('behind the scenes', as it were) may have ticked off the Shivans, resulting in the "Great War".
Here's an odd thought: Maybe the Hammer of Light actually did somehow ally themselves with the Shivans, or at least, by their very different behavior(for one, apparently refusing to defend themselves against the Shivans, as demonstrated with the Ramses) convinced them that the HoL was a different entity from the Vasudans proper, and(among other things, perhaps) were 'given' plans or a prototype of what became(for the Shivans) the Nahema, to reverse engineer, and give them a technological boost against their mutual enemies. The HoL took most of their secrets to the grave, but the PVE was able to recover some of the prototype Sekhmets, and noted that they had some commonality with Shivan technology.
If the FS2 Shivans were of a different 'hive', it's possible the Trinity may have panicked and fired first, and that was the trigger that initiated the "Second Shivan Incursion".
Whether truly the case or not, still very interesting...