"they have nasty fans" is certainly based off of perspective. Never been to Manhattan, but as with any visiting sports event, a ton of that depends on where you sit.
I would imagine quite a few of those problem children were those that don't know how to handle a rise to competitiveness such as the rise K-State had when all of a sudden they were competing on a national scale after decades of being an "easy win." When new to such things, they may not know how to handle all of a sudden being winners.
In person, every K-State fan I've known has been a very laid back, cool individual, and generally objective. The other nice thing is they generally knew quite a bit about all teams, not just their own, showing a lack of myopia that infects some fans of certain school. I can say the same of NU fans for that matter.
The only fanbase I've found that is generally truly obnoxious in person as they are on the smack boards have been the Aggies and Sooners.
Coincidence? Probably not.