Would I be right in saying that an introduction of this nature could go either way ? ... I mean, it's a delicate balance, or maybe just my skewed perception of things
Quite nice really - and I would also presume the sender knows both parties well enough to know how this email would be received.
That's assuming that the authors knows that they both actually do appreciate this type of humour. I'd think that if they had that level of familiarity then it would be expected that any email would get reasonable consideration or a phone call would be another possibility.
that was the case one would assume that the author could also have just called on the phone.