That's a really good possibility, and one I hadn't considered.I go back-and-forth about whether he was probably meeting someone or just avoiding bullies on the bus and then taking a day off from school to see London.
I have no doubt there were probably boys at his school who were the opposite of nice... So I do think he may have been compelled to just get away for a day.
If Andrew decided last minute (or at most the night before) to cut class in order to avoid bullies, then there would be no connection between him and whatever individual he may have run into while in London. And cases like these, according to police, are the hardest to solve.
This could explain why Andrew reportedly seemed "irritable" in the morning. Maybe he was debating like "Am I really going to do this? But if I don't, then I'll have to deal with those bullies today..." Maybe he chose that day because it was a Friday, so he could have three days of peace to himself.