This is a map of this morning's low temperatures. All of the temperatures in central Kansas were record lows.
Keep in mind these are temperatures five feet above the ground and it is the actual ground temperatures that matter when it comes to damaging the wheat crop. As a general rule, wheat is harmed if it is at the "jointing" stage (where the grains of wheat begin to form) and the temperature is 25° or colder. In Oklahoma and Texas, a majority of the wheat is at the jointing stage. In Kansas, it is less than half but a lot of the wheat is right on the cusp.
The areas that received heavy rain the last two days (see below) may have gotten a lucky break. When water freezes, it gives off heat. In the citrus belt, they spray water on the oranges and lemons hours before they expect a hard freeze. So, the wet ground might have served to protect the wheat to a point.
UPDATE: Additional information from AccuWeather.