Xenophobia is probably higher than it's been in centuries in Niops these days. Acts of violence towards FWL refugees back in the 3080s is a good sign of that, as are the protests outside the Republic embassy.
But, no, it also isn't surprising. Other than the occasional raid attempt by dump pirates or bandits that undoubtedly ended horribly, Niops' history had been relatively peaceful. Even the Capellan refugee absorption was relatively peaceful.
Then you have an influx of FWL refugees, a failed raid by the Marians, a coup attempt backed by a foreign merc unit, a successful Marian raid, a civil war, an invasion and nukings by the Word of Blake, an imposed embassy and attempt (likely) at a banana republic by the Rim Commonality, the Republic deciding to plant an embassy (which may have actually gotten the Rim Commonality to finally leave), and enough unrest during all this that it's nearly 15 years before you have elections again.
Is it any wonder they're paranoid? Throw in a suspicious shift in Marian policy from raiding and conquoring to "no, really, we want to be your friend" and the FWL getting the band back together...
Actually, know who Niops would probably get along great with? The Regulans. Aren't they keeping independent from the nuFWL, and still having their hate on for the Blakists?