More advanced combination/partition set questions will introduce sets with elements that are individually distinguishable. This requires the student-mathamation to discern the relevance.
For this question, the five could all be different or they could be genetic clones; it’s irrelevant to the question. For this question, they are Manoj’s friends and are indistinguishable from each other.
Of the six friends, only Manoj is distinguishable from the other five. He is distinguishable for the others because he will only attend a class if (and only if) at least one of his friends also attends. This is why he is separated (distinguishable) from the others. The other individual characteristics of the set of friends are irrelevant.
Here is a link to a question requiring discernment in what is distinguishable and indistinguishable for the solution set count. There are two distinguishable sets in this question and the elements of each set are indistinguishable from each other. The correct solution requires the two sets to be treated a one set of indistinguishable elements and partitioned. (I note you’ve already commented on that post).
GA