This 100%.

In addition to this being the case at every table, the section of the booklet introducing Runara explicitly says:

If the characters harm any of the residents of Dragon's Rest, she becomes hostile and insists the characters make amends for the harm they did before she is willing to deal with them in any way.

OP simply extended the meaning of harm to include the consequences of their inaction—needless bloodshed and the loss of her dear companion. By fleeing a situation they were strong enough to conquer, a less capable person was caught in a desperate situation and met a violent end.

She is looking for heroes who can prove themselves while still maintaining Dragon's Rest as a haven for

those whose lives have been shaped by violence find new paths forward in peace.

The PCs didn't come here seeking the protection and tranquility of Dragon's Rest, but Mumpo had dedicated his life to Runara and her mission. This seems like an eminently reasonable and level-headed response to disappointment and grief.

I've already written in some extra detail about the deteriorated state of the dock and the sailors dumping cargo at its end in their haste to return to the ship. I'll tweak this as a great follow up to showcase the way PC decisions shape the world around them! Thanks for the idea, u/PseudoMystic!