"Is he ill?" members exclaimed.
"No, I'm dieting," the self-confessed gourmand growled when asked the same by FE Focus.
There is no doubt that what the AoC chief executive lost in gravity he gained in gravitas during almost four years at the helm of a once deeply troubled ship. This year saw his best, most polished performance yet at the Birmingham conference.
He has climbed a steep learning curve from principal of City College Manchester to head a national office, sparring with ministers and union bosses.
Now, with the ship on course, a record pound;1.2 billion government funding increase, wounds with members healed and best-ever relations with the unions, he is quitting. This week, he announced his decision to retire next August when he reaches 64.
So, again, that question: "Are you ill?"
"Definitely not. There's nothing indicative of ill-health."
And that is the way he intends to keep things. He had discussed it at length with his wife Carol (principal of Waltham Forest College) and his children.
However, he refuses to be written off just yet. There are still issues to clear up relating to Education Secretary Charles Clarke's grant letter. "There is the need to develop trusting relationships, develop new targets in partnership with the Government and build an open and transparent funding mechanism.
"But, from August, we should be looking to the next general election. What do we want of future policy, from the next Comprehensive Spending Review and other policy developments?"
He has no doubt that his replacement must come from within the sector. The success record of appointing principals to top jobs has more than proven its worth.
Chris Hughes (Gateshead) took the Learning and Skills Development agency to record successes. Janice Shiner (Leicester) took the top post of director general at the Department for Education and Skills. Sue Pember (Canterbury) heads the Adult Basic Skills Unit, and Jane Williams (Wolverhampton) is the post-16 standards tsar.
It is a far cry from the days of the disgraced Roger Ward, who resigned as chief executive after FE Focus revealed details of secret consultancy payments.
Mr Gibson took over an organisation deeply distrusted by government, the unions and even its members. "It was internecine war at the time of Ward. At least now we are not trying to rip ourselves apart. I have tried to build a reputation for professionalism and integrity. Have we succeeded? I desperately hope so."
Tributes to his work include those of John Harwood, chief executive of the LSC, who said: "The way relations between colleges and the LSC have developed under David now forms the base for a true partnership."
And the future? Mr Gibson said: "I could always sign-up for an advanced cookery course at Birmingham College of Food."