As always with incidents, there's a multitude of potential causal factors which only the subsequent investigation will be able to determine resulted in the gear collapse.
That said, leaving aside, for now,
possible maintenance / manufacturing error it would come as no surprise if more than one form of corrosion was discovered as has been the case many times in the past with similar u/c failures. This might help offer an insight therefore .....
https://www.aircraftsystemstech.com/...corrosion.html