No, it wasn't. The race condition caused First Energy to not notice that their energy grid was one more line trip away from catastrophic failure. But there were four line trips that day caused by power lines hitting trees and shorting, the last of which triggered the dynamic instability that caused the blackout. First Energy had a whole host of issues that together caused the blackout, and the race condition in the alarm monitoring system was but one of them.

The full report is actually an interesting read. Essentially, the key problem that caused the massive cascade was that the line trips meant that large loads of power had to reroute long distances to get to the Cleveland demand area, and the non-infinitesimal amount of time it takes for the power to establish that route caused several lines to trip, to the point that the demand was cut off from the network before the supply surge reached it.