It's basically the word for word consensus advice of decades past. At least two generations grew up in a world where "take out the biggest mortgage you can" was considered good advice by default. As history has proven that is not a consistently successful approach for individuals and has some pretty severe trade-offs at the societal level. I'm not sure if it was the point he was trying to make but in any case it should probably serve as cautionary tale that consensus is not necessarily correctness.
But we're discussing the group consensus of a self-selected group of people interested in finance, who are nerding out about it on the internet, not the group consensus of the general population.
"Take the biggest mortgage you can" became known by the general population because it was repeated again and again by every financial literacy magazine, talk show and newspaper advice column back in its day. If anything that is an even more refined interest group than Reddit because you needed more than an internet connection and an interest to get into it.
