Thanks, I think I understand the comment now as:
"We weren't holding the jib sheet as we never normally do that. It was, in hindsight, a mistake".
The takeaway being that in conditions where it may be necessary to dump the main, be prepared to follow that by immediately dumping the headsail too.
If one issue was that the jib overpowered the rudder, surely holding the jib sheet is a good thing so it can be released more quickly? Or have I misunderstood the comment?