But it was not Mr Amenya's leak that actually changed the government's mind.
It was only when the US authorities indicted Gautam Adani for alleged involvement in a $250m (£200m) bribery scheme that Kenya acted.
Representatives from the Adani Group denied the allegations from US prosecutors and called them "baseless".
At a state-of-the-nation address in parliament last month, Kenya's President William Ruto announced the cancellation of both Adani deals.
"In the face of undisputed evidence or credible information on corruption, I will not hesitate to take decisive action," Ruto said in a speech met with loud cheers inside parliament.
Kenyans celebrated the decision which Ruto attributed to new information provided by investigative agencies and partner nations.
"I was in class when this announcement came. I couldn't believe it," Mr Amenya says.
"I think in the first one hour, I had tears in my eyes. I was so happy."
Although he does not see himself as a hero, messages of support poured in from everywhere, including from India.
Forty minutes after the class ended, he posted his now-famous tweet "Adios Adani!!" - goodbye Adani.
"It was momentous… All that I did finally paid off."
The feeling of triumph, however, came after months of personal struggle and pressure.
Soon after exposing the airport deal, Mr Amenya was sued for defamation by an Adani Group representative and a Kenyan politician, making him question whether he should continue.
"Some people were coming to me from the government, they were even ready to pay me, they were telling me: 'You need to cash out and just stop this fight with the government,'" he recalls.
"It would have been the biggest mistake of my life to give up, a betrayal to the Kenyan people."
But even after scrapping the deals, President Ruto still questions why Kenyans opposed this and many other projects he has championed. He says he will find a way to upgrade the airport.
"I saw them saying that those who stopped the upgrading of our airport are heroes. Heroes? What do you gain when you stop the building of an airport in your country?" Ruto asked at a public function in early December.
"You have no clue how it's going to be built, and those who are opposed have never even stepped foot inside an airport, you just want to oppose."
Mr Amenya, who is still facing the defamation cases, is now fundraising to help with his legal fees, and says his future in Kenya is uncertain.
"I have received threats from credible intelligence agencies and people in Kenya that have warned me not to go back because obviously there's some people who are very angry with what I did," he says.
A hefty price, but one Mr Amenya says he would gladly pay again.
"We don't really need to wait for someone to save us," he says.