Oh, yes, your son must feel very disappointed. I'm sorry. But have you looked at the courses/modules of other courses in detail?
My DS is going to do CS (joint with another subject). They'd already got results (IB) and had done well, and could pick from quite a few higher ranking unis.
However, after looking at the modules and courses, he went with a mid-ranked one as the course was so much more interesting. The town it's in also contributed to the choice., connection to others, transport, the surroundings too - all so important.
And yes, I get what you're saying about international fees and it being unfair.
My DS's first choice was a course at Edinburgh and there was room in clearing, he had the grades, a great PS that fitted well. However, only one course (nursing) is open to RoUK students and 254 were for international fee-paying students! The fees for the course my DS was wanted way almost £35K!!!