Tired and emotional is a semi-polite or humorous euphemism for drunkenness, but in this context it is implying that Sean's father was not drunk at the picnic.
Consider the statement "“I might be mistaken, but Sean's father looked a bit sober and level-headed at the picnic, didn't he?.". Is the statement "“I might be mistaken, but Sean's father looked a bit tired and emotional at the picnic, didn't he?" false? Yes/no/unknown