Pro-government lawmakers walked out of the chamber, failing to cast any votes, later blaming it on a fellow lawmaker who was ill and had asked for a 15-minute break.
Twenty-eight legislators voted against the controversial proposals. Eight others voted in favour.
"Pro-establishment [lawmakers] say they walked out because they were waiting for Lau Wong Fat to turn up to vote," tweeted Steve Dunthorne, a journalist in Hong Kong.
"Three minutes left, where is Lau Wong Fat?" asked another.
Representing the New Territories, veteran Hong Kong lawmaker Lau Wong Fat has been formally identified with the pro-Beijing camp.
He has recently begun to wind down political activities.
"I tried to rush back. I feel bad in my heart. I'm sorry," Mr Lau told reporters after Thursday's vote.
He also said that he had been feeling unwell earlier in the morning.
But social media users in the territory did not buy this excuse and took to Twitter to express their views.
"[The] establishment would choose waiting for Lau Wong Fat as an excuse when he has the worst attendance record," said Twitter user Larry Au.
Another user Isabella Steger also shared this meme, explaining how Mr Lau had taken the fall.
A Facebook page titled "The Wait for Uncle Fat" attracted at least 3,000 likes in the first two hours.
The parody page, which also shared several memes, videos and jokes about the politician, drew a stream of commentary from Hong Kong users.
"Don't worry Uncle Fat, you actually drove away the rest of your Chinese loyalists! Thumbs up for Hong Kong," said one user.
Another remarked: "Let's not pick on Uncle Fat today. His absence today was totally excusable!"
"I wonder how much Uncle Fat's vote would have meant even if he showed up on time," wondered another user.
There was unexpected drama moments before pro-democracy lawmakers in Hong Kong defeated plans for a Beijing-backed election reform on Thursday.