It seems like OP's husband or OP herself has also some issues re. letting a stranger come to their house. Thinking of a couple of perfectly decent Swiss youth who have watched mine now.....I personally don't see (again) what's the reason for this anxiety.
But I think we may not get the whole picture....Understandable.

It was maybe unfairly written. He told her to call her if she needed him, then he went somewhere he knew he would have no phone signal. So she tried to call him. When he came back he said he had meant that she should go into the garden and shout for him and thought she would have realised that Of course, as they've been told by me never to go out unless there's an emergency she didn't, and she had no clue that you can't call a mobile if there's no signal, nor that because of where he was he wouldn't have a signal and she saw him walk out with his phone.

Childlock on and yes, I've been through this with them.

basically because he is as he is. I don't say his classmates are unkind to him or anything, they're (mainly) a nice bunch and look out for him, but they don't go out of their way to play with him or want to meet up with him out of school.

This is not unusual here at all, I see it every day. And it is not always "because of the kids who don't fit in" but because the acceptance and integration of mildly unusual or peculiar phenomena is usually low/slow, here.

Btw, don't feel like you have to, by any means, justify to a group of random strangers online.

The situ does call for arranging some long term solution with sitting, though, for you guys. So you two could have a date, get out a bit, etc.

As per schools organizing meetups without kids, we had it all - with our kid, without, all teachers, just the class teacher, all parents, only mom/dad, etc. Usually local system counts on grandparents stepping in and sitting, which is logical.

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"L'homme ne peut pas remplacer son coeur avec sa tete, ni sa tete avec ses mains." J.H.Pestalozzi