Well the NYT has an article about it and it all started with a power outage. That
outage caused a domino effect on trains across the NYC Metro area.
snip
The power failure occurred at 7:30 a.m. at the Seventh Avenue station, at 53rd Street.
Because it knocked out the station’s signal system, most of the trains that stop there, on
the B, D and E lines, had to be rerouted to other lines. Gov. Andrew M. Cuomo said the
power loss had resulted from a Con Ed equipment failure.
Any train that was not rerouted had to be manually directed through the station, a particularly
time-consuming process, according to the Metropolitan Transportation Authority, which
operates the subways. Because the system’s lines are so intertwined, a ripple effect
was almost inevitable. A spokeswoman for the authority likened it to cars being diverted
from a highway to local streets. Gridlock ensued as other subway stations dealt with
the resulting overflow.
end snip
https://www.nytimes.com/2017/04/21/nyregion/manhattan-power-outage-subway-commute.html?_r=0
Was it a problem? YES, IT SURE WAS A TRAFFIC MESS!
Could ALL subway trains be rerouted? HELL NO; IT CAN'T BE!
And the ONLY lose of power was in the subway system.
But go ahead, take the N.Y. Slimes' and CBS' word for Gospel, but I hope that you have a huge stock of Reynold's Wrap handy. ;^)