The article you link from NPR seems to mostly cite the Haaretz article. The only possible corroboration are the claims from Adil Husain, but I am hesitant to take his words as corroboration.
The Haaretz article states it is unclear how many died from IDF fire vs the Abu Shabab group. Husain was not at the aid site and so can't state how they were wounded.
If the soldiers truly fired on those who were only running away, not advancing, this should be investigated and charged as a war crime. However, at this point the evidence is not clear aside from a handful of anonymous sources from a single press release.
The Haaretz article states it is unclear how many died from IDF fire vs the Abu Shabab group. Husain was not at the aid site and so can't state how they were wounded.
It is also the case that doctors without borders is far from a non-partisan group and has harbored terrorists in the past (e.g. https://www.timesofisrael.com/idf-slain-gazan-named-as-docto...)
If the soldiers truly fired on those who were only running away, not advancing, this should be investigated and charged as a war crime. However, at this point the evidence is not clear aside from a handful of anonymous sources from a single press release.