Please help with this behaviour

[belay]

My ds is 13. ADHD and some learning disability. We had an appointment at the neurodisabiliy clinic today. It was lovely sunshine so he walked back home (short distance) When we got back home he sat relaxing on the sofa for an hour or so. When my husband arrived home from work, he suddenly went to get changed and shot out, saying he was going for a walk. We said no, it was dark by then but he went out anyway. We could see him on the tracker app and he was getting quite far away. I rang him and he said "don't ring me" and put the phone down. He was heading away from home and then he turned off his GPS. I rang the police, they were brilliant. It took quite a while to file a report and as I was on the phone he arrived home. I gave him some water and then ignored him, as I did not want him to disappear again. In the meantime, my husband had seen the police looking for him and had a talk to the officers. Since coming back, ds hasn't spoken about it at all. He said one very quiet sorry and doesn't seem to realise how much we were upset and worried !
Why this sudden urge to go off walking ?
And why when he's been told not to do it?
He had already had PE and a walk that day so it wasn't like he hadn't had any excercise.
The police officer rang and text him when he was missing and I am now wondering what would have happened if he hadn't got that call and text???

Could the walking be his way of processing what had happened in his day, particularly if something said at the appt had upset him?

I knew an adult with AS and he would 'have to' go for a usually very long walk whenever he was overwhelmed, it was the only way he could deal with life's pressures.

BlankTimes thankyou. He's wanting to walk and explore but doesn't grasp the safety concept. I asked a youth volunteer to visit yesterday to chat about it but all she did was log it onto a laptop. No advice given 🤔

Can you get her to come back and do what you asked for in the first place? Maybe if you say it's a safeguarding issue you may get a better response - I'm not sure of the exact definition but it should cover a vulnerable kid with ASD walking alone in an unknown area, especially one who needs someone other than in his view nagging parents to explain how what looks okay on the surface may have very real hidden dangers.

Ask around, places like NAS and NSPCC should have leaflets or videos that someone he relates to can build on. I've had a quick look on youtube but nothing I found seemed to fit the bill for a teen with ASD or AN, maybe a better search would be a starting-point.
these are basic
www.nidirect.gov.uk/articles/keeping-young-children-and-teens-safe-while-out-and-about
www.areavibes.com/library/street-safety-for-kids-and-teenagers/

In this day and age, there must be some great resources online that would appeal to him and inform him at the same time.
I don't have FB or a local group, maybe there's something in your area.