Should they be lumped into the same category?
Are they different?
The answer is YES, they are different and should both be considered for teaching.
We can play on our own and could have tons of play skills, but not have the ability to interact with others for those activities.
Likewise, we could be very social and attempt many interactions per day, but not have the play skills to continue the interaction.
The important thing to remember is to analyze the behaviour.
Using an assessment like the ABLLS-R, which breaks the skills down in to two sections, will help you determine the exact skills that requires teaching.