What she means:
In many ways King of the Hill had exceptional continuity for an animated series. Nancy gradually grew to fall back in love with her husband and stop cheating on him, Connie and Bobby go from being friends to in a romantic relationship to just friends again, Luanne's hair takes several episodes to grow back after it was burned off in the supermarket explosion, and there are frequent callbacks to earlier episodes. However, one glaring inconsistency is with the Souphanousinphones. They are introduced in episode seven of season one when Bobby has been established as being 12 years old, but in later episodes there is more than one remark about them living in the neighborhood for seven years, even though Bobby only ever ages to 13.