I'm on completely the other side of the fence. This could entirely have been done with the best of intentions - they knew they were unable to meet his needs, knew that there was at least a possibility looming of exclusion, and were discussing placements which might be more suitable.
Presumably if a place had been available, and had been possibly suitable, you would have got a telephone call requesting a meeting to discuss the possibility. At that point you could all have worked together to visit, discuss the placement, look for other possibilities etc.
I'm not sure what the problem is. I'd be quite happy for an educational establishment to be pro-active about where my child's needs could be met, particularly if they knew they weren't meeting them.
Much rather that way than ignoring the fact that they were unable to cope and leaving the child to fail in situ.
I'm sure it would be important for those concerned to know that this hadn't been discussed with you - I don't see it as sinister. I see it as a care taking so that you didn't get a phone call from a well meaning LA dude who opened with 'so, about x going to y school...' Rather than someone contacting you and saying 'hello, x's current school are struggling and we would like to meet and discuss a more appropriate placement.'
I would be reassured that they had ds's best interests at heart and were looking for an alternative placement. I'd actually be more ticked at the LA who knew the school were unable to cope, and did nothing.