1)incident happened on 16th, while you returned on 17th, so naturally you didn't realize much about it. The article itself says that the whole thing happened during night time, and the last train at Panchrukhi is at 21:54, plenty of time for train to derail at narelu, bring in loco to haul the train out ward and resume normal operations. since this track doesn't see heavy freight/pass activity there was no 'ripple' effect on trains hence by next day everything would have normalized.
2)lack of RB acceptance+newspapers general lack of interest towards HP meant you didn't see the news much
3)derailments...
more... do not necessarily happen due to speed. Even Matheran toy train derailed some years back, and that train barely reaches into double digit speed. Inclement weather, poor maintenance, aging infra all are the cause for it.