I'm inclined to agree. The Duke is very old, still working, and, I suspect, not very well these days.
I can't believe that Jamie Durie would have been other than respectful and delighted by The Duke's interest, just as he was so ecstatic that Her Majesty had spent 10 or 15 minutes with him complimenting him on his gold medal and asking questions about the garden's design. In hindsight, it might have been better to not tell the Duke that the plant was a cycad, not a tree fern, but Durie was probably most chuffed at getting this very valuable plant from Australia to Chelsea without damage and still healthy and flourishing. Jamie Durie has already said that he didn't hear The Duke's comments.
I've heard reports here that Her Majesty was presented with an Australian bottle-tree after admiring them; likewise Prince Albert of Monaco who was taken with this lovely Australian native, too.
I understand that all of this has been filmed and will be shown on Australian television tonight so it will be interesting to see just how much of this report is factual and how much a Daily Mail beat-up.