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What happened? A mathematical puzzle

Suppose we have a party with 90 Sololearners. Given are 6 tables. So at each table we will have 15 Sololearner. VcC asks all Sololeaner at the party to hold the following rules: Every Sololeaner should sit at a table with 7 persons he knows and 7 persons he does not know. (If a knows b, b knows a too) Afterwards the buffet will be opened. And it is the best one the world has ever seen. Sebastian suddenly takes a glass of wine, a pencil and a sheet of paper. Afer half an hour and 2 promille he passes the paper to Oma Falk. Both smile, leave the party and go to Mc.Donals for some Chicken Mc.Nuggets . Btw: ChillPill ist just ordering 11 nuggets. Why did they not wait for the buffet?
See comment for link for solution.

Omas Puzzle