Paddy – your Executive Committee and its Strata Manager have done precisely the correct thing in all respects, both procedurally and legally!
It sounds to me like the new tenants may be are aggrieved by the fact that they received the Owners Corporation’s advisory letter so soon after moving in, and in circumstances where they may well have been in the process of unpacking and moving things out of the garage to make room for their vehicle.
Irrespective of the fact that some Lawyers like throwing their weight around by the use of legalese such as “incendiary action” because they think that impresses and/or intimidates the recipient, if this one wants to additionally distribute his correspondence then I suppose he could do that by way of a letterbox-drop to other residents/owners, but the Owners Corporation has no obligation to do anything more than to ensure that everyone who read the advisory letter reads the response, or to in future correspond directly with him or indeed any other tenant unless of course it chooses to; so again you’re on firm ground both procedurally and legally.
He’s blown of steam in an effort to cover his embarrassment, so just ignore him, and hope that the vehicle soon fits inside the garage – because those By-Laws do apply!