Well... are there people who were young UK teens then, had kinda similar interests to Andrew and could offer their insight as to why THEY would do such a thing?
Maybe he didnt. Impossible to rule out that in his mind he would be able to either call home with explanation or came back before they will realize he skipped school.
My husband is actually very similar to him. Even now, he keeps the same hairstyle he had back then! Looking at his personality, he was never a "rebel." He would never have snuck out to a gig; he was the type to ask permission, and if his parents said no, he simply accepted it. He doesn't quite understand why Andrew would suddenly break character that day, but he did note that traveling to London young wasn't necessarily seen as "risky" behavior back then.
My husband was allowed to travel to London for gigs or the cinema in Leicester Square even before he was 14. Coming from an American perspective, the level of independence in Europe can be a culture shock. It's common for kids here to use public transport alone from a very young age like my goddaughter in Germany so Andrew being in London alone might not have felt like an "extreme" act of rebellion to him. My husband thinks the answer lies in the reason as to why he went that day and during school. He can't imagine ruining his perfect attendance record because that would annoy my husband. And my husband notes he never got train tickets without a return because he knew it was cheaper and under 16 tickets were a thing he would buy. Generally a lot cheaper than adult ones. He remembers paying like £13 back then for tickets to London from a similar area/distance to Andrew.
Personally, I was a "rule-follower" too. I grew up watching kids on sitcoms like Full House sneak out of windows and I thought, "I’m never doing that; I’ll get caught!" I had a very peaceful upbringing where my parents never even raised their voices, so I can't imagine the mindset of intentionally upsetting that dynamic. I never had chores. I never got told off or grounded. My mom did the dishes and laundry. My dad vacuumed and took care of the lawn. My only job was to be a kid and have fun. I stayed out of trouble. I never snuck out or did drugs or underage drinking or went to parties. I knew I could do it because I had a friend replace water in her water bottles with vodka when we were 12 because she liked the way it made her laugh. Her parents never questioned the missing vodka or replaced version with water. It just never occured to me or was on my mind. Never thought about it. Was never curious about rule breaking.
However, this leads me to another theory regarding the timeline of that day:
We know from interviews that Andrew’s parents assumed he was home gaming or in his room because his blazer was on the chair. They didn't realize he was missing until dinner. If it was normal for them to come home and not "pop in" or speak to the children immediately, it makes me wonder: Is it possible this wasn't the first time Andrew wasn't where they thought he was?
If Andrew had a "private life" or was meeting someone locally, he may have realized he could be gone for hours without anyone noticing.
Saying no over the summer might explain why he didn't want to go away that summer—he had something or someone keeping him locally.
If he had ever been caught "not home" previously, he likely could have easily explained it away as being at a neighbor's house.
We often see in these cases that even the most "predictable" kids can have an entire world their parents know nothing about until something goes wrong.
While his family might find it impossible that he was sneaking out, they likely felt his disappearance was impossible, too. It’s a tragic reminder of how easy it is for a teenager to create a private space, even in a loving home.
So maybe he was sneaking out prior and nobody noticed because on the day he went missing they didn't go to his room straight away to check in and say hello?