Is FKS my fault??

I rescued two nursing moms who had ten kittens between then. Moms and kittens were doing great, the kittens were gaining weight every day and growing into energetic little nightmares lol Then suddenly two of them passed away. They were five weeks old. In the last week, all but four kittens have passed away. Vets in my area diagnosed them as having FKS as, despite professional intervention, they weren't thriving and surviving. Three of the remaining four seem to be doing great still, very active and eating well. The fourth is struggling, as she's always been very tiny compared to the others. I'm following vets instructions to give her a fighting chance. The person who was helping me locate a shelter who could help me get them adopted out has now told me, after I told them what was happening, that it's 'not my fault' but continued to berate me about not immediately taking them to a shelter or rescue (despite both of us knowing space was extremely limited, there's wait times and you have to set an appointment to surrender any animal and that I was in contact with a rescue and waiting to hear back), that I should never do this again, they should have 'demanded' I surrender them. I've been rescuing cats for years and know what I'm doing. I've dealt with things like this before but I've never been accused like that and now I feel like it is my fault these kittens didn't thrive despite every precaution myself and the vets were taking. I don't even know how to respond to this person after them saying that to me.