A head gasket, or any other cause, will not "blow" a radiator unless it's weak, anyhow. The rad cap will blow off pressure. So, don't know what your cause is. Might be more than one.
On inspection the top seam had been resoldered and only a small strip of the solder had reattached to the core.
You could see the new tear line in the solder where it ripped loose.
