Single token only works when trains always alternate direction down the line. Apparently there was an extra train in one direction in this case. That's not to say there aren't simple reliable methods, but single token isn't it.
Telephonic Block signalling was in use here.
https://en.wikipedia.org/wiki/Signallin ... onic_blockIt would appear the station staff at Andria confused a late running earlier train with the train still on the track (which was also, necessarily, running late because of the train in front), and cleared the south-eastbound train thinking the line was clear. The late running first train would appear to have departed at the time the second train was due to, if it had been on time. Very hot (40), sunny, just before lunch - a known nadir point in human awareness. A cynic might think the station master couldn't be bothered to interrupt his pre-lunch nap for long enough to do his job properly, and just waved off the train onto the single line after a glance at his watch, or got his coffee boy to do it for him. Trains collided on a curved section of track in the olive groves, so impossible to see clearly ahead.
Funding was approved over 4 years ago for doubling the line (only section remaining to need it), but had only just been put out to tender. A cynic might think the four year delay was so that appropriate recompense for officials could be negotiated before whose cousin would "win" the contract was decided. But that's cynics for you.