I'll disagree with this statement after living in both cities.
San Francisco is FAR worse than NYC when it comes to homeless people. Matter of fact, after like my first month living in NYC I told my girlfriend that I was amazed at how few homeless people I saw. I've gone whole days in NYC without coming across a homeless person. In SF I couldn't go more than an hour without stepping over a bum or having someone ask me for change. And that's on a good day. Most of the time you encounter a bum every 10 minutes.
From a numbers standpoint I have no idea the amounts in both cities. But from a personal experience standpoint I encountered 5x as many homeless people in SF, as I have in NYC.
