As the rules dictate that, if you are part of the same family (i.e. living under the same roof) the distance suggestion doesn't apply, surely the same should apply here? It's the crew of a sub! it's not like they're taking on passengers.
The article doesn't say that at all, in fact it specifically says:
"The source said the barbeque alone - for a crew that was back for a short period of maintenance on the submarine before heading back out to sea - would not have triggered an investigation, but that it followed a number of other alleged "errors of judgement"."