Mate,
I think the safety of any crew is important, and if you were running a trip and I asked to come along without you knowing me, I would expect questions to be asked.
Griff is one of the most active paddlers in Canberra, and also the keenest to have new paddlers along, he's put countless hours volunteering his time for beginners, I don't think what he wrote he was calling you an idiot in any way.
I think your rocker would be fine.
Cheers
Mick