This appears to be the original leaked story:
http://www.nydailynews.com/front/story/433227p-364959c.html
Schumer was not mentioned. The other stories' writers probably called him for a comment after the Daily News story broke.
The Daily News story is interesting. By my reading, it is clear that the leaker told the reporters about the "flooding" of the financial district, it was not speculation by the reporters. Reason? Because in the same article it is evident the reporters questioned the flooding claim and checked with experts about what the leaker told them. They fact checked a leaker! Doing their job.
Obviously, collapsing a tunnel under the Hudson (if it can be done) wouldn't flood the financial district. It's not beneath sea level. Even Schumer knew that...
However, flooding a subway tunnel under the Hudson would have a chance to flood many of the subway tunnels in Manhattan. Many (if not most) of them are certainly beneath sea level.
Thus, the logical choice for an attack would be the PATH tubes. That the leaker couldn't figure that out suggests a minimal level of information (and intelligence).