Looks like he was “smart” enough to mortgage the whole amount; otherwise he would’ve lost his down payment when he walked away.
I think this guy took a risky bet and lost. I certainly wouldn’t have done what this guy did, but I don’t think it was “stupid”. My parents stretched financial to buy their first house (and broke the “golden rules”) when they first got married, and now it’s all paid off and it worked out really well for them. They saved tons of money by not buying a starter home and upgrading later, and bought their dream home right off the bat. I think the golden rules, like all generalizations, are just guideline/suggestions. Only you know your own risk tolerance level best.