Hayabusa and Komachi trains somehow detached

Just saw this on the news (Japan) this morning, Hayabusa and Komachi detached.  Fortunately, no injuries.

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Wow...how fast was it going when detached? Mechanical failure or human error?

And for illustration, yes they indeed used Plarail trains to recreate the detachment.
(They didn't even try to couple them even though couplers exist on the trains)

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Must have been going pretty slow if the trains stopped so close. Which is fortunate as, if it was going as fast as it can it surely would have been a major disaster.