That is part of it, yes.

Also, the mechanism of addition itself often causes the harm. With chemical addiction, the same components that make the substance addictive also cause miserable withdrawal symptoms.

With social media, this is more nebulous, but I do think part of what makes systems like Facebook "engaging" is the anxiety they create when you aren't on them, and the low self-image that users try to assuage by posting flattering photos of their life.

Part of addiction (and advertising too, for that matter) is creating a need for your product in the mind of the user. They were probably happier before they had that need in the first place.