If the reporter's version of events is to be believed, (I admit, there's no guarantee his rcollections will prove to be accurate), the two aircraft seem to have been on reciprocal tracks on the same airway, so one single mistake by one person, be it a controller or a pilot, was enough to cause this tragedy when coupled with some as yet unknown malfunction to a TCAS system.
Long time Ppruners will be familiar with these threads from the very early days of Pprune.
http://www.pprune.org/go.php?go=/pub/tech/MidAir2.html
http://www.pprune.org/go.php?go=/pub/tech/MidAir.html
This stuff was written ten years ago, (I know, because I wrote it), and still there is amazing resistance within the industry from pilots, ATC and regulators to offset tracking.