I suppose the most fundamental part of this argument is why this individual believes that social media does not promote social interactions and/or belong in higher education, as well as your personal stance on the topic.
With the definition provided, social media would be very apparent to promote social interactions (even the word interactions is in the definition given.) For your response, it would be good to consider whether or not you agree with this definition of social media; if so, you would be against this person's argument and you have a clear basis to argue why not. If you would redefine social media to not involve interactions, then you would agree with this person's argument.
For the second part of the argument, you should consider why or why not you believe social media is/is not fundamental to higher education. For example, I may believe social media is important to higher education because it stimulates ideas and collaborative thinking, while the opposing side may state that it also encourages cheating and provides methods of breaking the honor code.
This can be illustrated in a fantastic way and you should definitely consider your own perspective.