this is what i think happened the guy had been stranded on an island with 2 other people. while on the island the 3 men had to survive. the three would starve if they didn't find food soon. The second guy killed the third guy and with the guy in this riddle ate the 3rd guy calling the soup they made seagull soup. the man liked it, assumed the second died somehow then after he swam back to civilization, he went into a restaurant ordered his soup he ate on the island and upon tasting the difference, realized he had eaten his friend on the island. So thtats why he got killed i think.