Everything is D/s in some way or another. We work for someone and we 'obey' their directives. If someone works for you, they obey your directives.

Pecking order in social clubs, even the PTA. I'd bet even your ordinary friendships involve some sort of leader/follower relationship.

So, when extending it to D/s in this context, yes, it includes sex. Even if you never touch or meet or play online. Because for at least one of you, (and I'd argue both,) behind it all there is an accompanying sexual tension.