The fact the boy lied suggests he did not want his family knowing what he was up to. – no offense but well obviously, that's kind of the purpose of a lie.
She said: "If I'd have known [where he was going] I wouldn't have let him due to the winter weather conditions.
They are all sensitive, intelligent lads and we are just hoping they parked up, got lost and are OK."
Sometimes you can have a really healthy relationship and teens still insist on doing borderline suicidal things.
This isn't the same but say if an underage girl insisted on sleeping with a middle aged man – no mother is going to say "well I disagree but just make sure you stay safe dearie", which is why the DD wouldn't tell her mum in the first place. Or if someone were almost certainly risking their life as an inexperienced camper in harsh advanced conditions due to peer pressure, they wouldn't expect their parents to say yes. Etc etc