Requiring 50% in a referendum is different from and safer than requiring 50% in a parliament vote. A parliament can go against the people that elected them.
[1] https://fullfact.org/online/brexit-referendum-electorate-lea...
Anyway, I wasn't even trying to argue in favor of this position, or against it. I was merely replying to the parent comment that Brexit did not meet the threshold that their parent comment had suggested.