It is somewhat ironic that Palu got hit so bad, since it is one of the most sheltered places from the large m9 tsunamis.
You can see it right in the middle of all those huge subduction trenches, all of which can pop off an m9+ any old time.
What got Palu was an internal 'fault' or a large strike-slip earthquake. You can see the N-S gash of the fault. This is a weak zone that accumulates the strain of the whole area being pushed around. It would not be at the top of the list for a destructive earthquake. Palu is at the end of a bay along the fault, and had no chance. This was a very local tsunami.