WTF ? Cumbria plod going sorf■■■■■■■■■■■■■■■■
truck driver NOT arrested ■■?

It states driver not injured

Why should he get arrested?

it doesnt say he wasnt arrested

Seems to me that there is possibly enough evidence at the moment to suggest that the lorry driver is not at fault, hence the reason no arrest. From the news article you do not get any info that would lead you to believe one way or the other.
I agree that it would appear to be the norm for any driver not just LGV to be arrested initially when there is some evidence to suggest they are perhaps in some way to blame. We will just have to wait and see what develops over the coming weeks and months.