Most people that are not knowledgeable in underground music consider Chillstep a sub genre of Dubstep. In actuality it is a sub genre of Step.
Dubstep is a fusion of both Dub and Step genres (Hence the name).
Chillstep incorporates many of Steps movements, but adds relaxing undertones and rhythm to it.
Chillstep song examples;
Days to come- Seven Lions
Mitis- Innocent Discretion