Most young girls aren't out at 4. (I am calling 16 young too.) Maybe, as someone else has said, he might have found out more about the person he was hopping to have sex with, whatever her age, as a start. "Its late isn't it? What have you been doing tonight? Are you tired? Where were you going in the taxi?.. and so on.
She had been drinking too. He must have been able to guess that.
Scottish she cannot have looked so old that she would have looked like a woman who was so grown up it would have been an outrage to her more about herself - (question her right to have sex by implication, if that is what you are saying).
Better to ask an evidently very young woman out alone at 4 in the morning more about herself.
In a Ched EVans type case of the future, if police happened to see the young girl in the dark, all dressed up for a night out, and deemed her to look older than 16, then he would be able to be acquitted on their evidence if this is to be the standard.
Having said that, the verdict does not seem to mean he is completely vindicated, if I have not misunderstood. I do think it presents a dilemma
overall.