Calling the Caldari isolationist isn't quite correct; they don't care what you are doing so long as they believe you pose no threat to them. For some Caldari, this line of thinking is to make others so dependent on them that they can't afford to endanger their good relationship (this is the general way of going with regard to the Khanid and Amarr, for instance), while the other line of thinking, probably more popular among Patriots than Liberals or Practicals, is to assume that if they do threaten you, you can crush them militarily.
This doesn't mean the Caldari don't pay attention to what goes on in other places, or don't take action, overt or otherwise, against people, organizations, or entities they perceive as threats, but in general they try to create a situation where they are on top and then maintain that stability. The "isolationism" exists only in that they don't really care what anyone else is doing so long as the status quo remains. Amarr want slavery? Eh, okay, so long as the Amarr don't get any bright ideas about pushing it in Caldari space. Amarr want to start driving Caldari companies out of their market for religious reasons? Whoa whoa whoa...hold on a second there, buddy.
I think I better way to look at it is that the Caldari do not have a strong foreign policy agenda aside from "make sure our position is secure." Part of this is cultural, but there's also the aspect that the Caldari State is a very divided government, and each of the eight corporations has its own foreign policy agenda, and they often conflict. Whereas the Federation might have a "make the world safe for democracy" agenda or the Amarr a "spread the word of God" agenda that get them involved in things where there is not going to be any sort of substantive gain for them.