The Thai architect's studio, DBALP, won the competition to design a new terminal for Suvarnabhumi airport, with plans for a canopy of stepped timber arches that some online commenters have likened to Kuma's Yusuhara Wooden Bridge Museum in Japan.
The comparisons led Bunnag to defend the design. "I didn't copy anyone else's work," he was reported as saying by the Bangkok Post.
"Those who follow my work will know that I created a similar image in my previous designs, such as for a hotel in Sri Lanka."
His inspiration, he said, was the lush landscape of Thailand.
Covered by the soaring timber canopy encased in a glass facade, the design for Suvarnabhumi's terminal two features an indoor tropical rainforest complete with waterfalls.
In Singapore the Moshe Safdie-designed Jewel Changi Airport is due to open next year, featuring a giant dome with a waterfall pouring through the centre to the indoor forest below.
DBALP Consortium's design has a steel structure that will support timber beams, which will form a grid pattern and filter light like a rainforest canopy.
The competition to design Suvarnabhumi's terminal two was already controversial, after original winners SA Group had its contract revoked by Airports of Thailand (AOT) for failing to supply a document quoting the cost of the project.
DBALP Consortium, along with Nikken Sekkei, EMS Consultants, MHPM, MSE and ARJ Consortium, had originally been named the runner up for the competition to design the 35 billion baht (£822 million) airport.
SA Group is believed to be contesting the decision, claiming they did not receive the essential document from the AOT in the first place, and highlighting that its proposal was under the stipulated budget.
Bunnag told local paper The Standard he was "sorry" for his competitor's loss, but insisted that there had been "100 per cent no corruption" in the sealed bidding process.
Suvarnabhumi airport's terminal two, which will have capacity for 30 million passengers a year, is due to open in 2021.
In Mexico, the fate of Norman Foster and Fernando Romero's airport for the capital city hangs in the balance, after the country's newly elected president announced a public referendum on cancelling the $13.3 billion (£10.30 billion) scheme.