Just to play devils advocate here.
At 10 nm from Tangalooma as you state you had just made that call, you are actually halfway between Bribie bridge and Woorim and right over the southern part of Bribie.
At that point you at the juncture of 3 different frequencies, Caboolture/Caloundra 125.85, Redcliff127.15 and Tangalooma on 126.5. Most people in that area would be on the 125.85 as it is part of the eastern/southern training area for Caboolture and Caloundra. in that area I listen to 125.85 and monitor either Redcliff or Area.
Again most people that I know crossing the bay Bribie to Moreton and back do so at as close to 3500' as possible. In theory if the fan stops halfway across at that height in most aircraft you will have enough glide to get to one of the beaches so long as you glide with the wind behind you.
Even up to 3 miles out over water he may not have been crossing rather just flying local as many do head out over the water when flying around Bribie eastern beaches.
When I am crossing I do the following.
West to East I use the 125.85 from Ycab to Bribie and monitor 126.7
I give position and crossing calls on both 125.85 and 126.7 and a 10 mile call for Tangalooma over Bribie central.
I fly a 3400 and monitor Area and 126.7 and fly almost directly over the VFR Route.
East to West I use the 126.7whilst ever I am over the island and monitor area
I give position and crossing calls on both 125.85 and 126.7
I fly a 3400 and monitor Area and 125.85 and fly south of the VFR route from Combayuro Point towards Woorim. Once past halfway I swing North towards the VFR Route and cross the coast almost right on it.
I find that gives me the most options if the fan stops.
I do often fly around Bribie with no plan to go anywhere and sometimes pop out over the bay to check out a ship or boat or sometimes just a shadow without intending to cross.
One last point, below 5000' there is no requirement to even have a radio and as such we should assume that there will be someone out there without one. Best answer to that is eyes outside.
Not trying to justify anything here really other than that is a high traffic area and people may not be doing what you think they are doing or should be doing, but could still be well within the rules. FWIW