Water lily. I too am thinking perhaps the teacher was erring on the side of caution? I wonder too that not sitting still on a mat at 3 years old is considered 'delayed'?
I'm so sorry for your loss, and I can't imagine the impact that must have on your parenting. I agree with Spring, though, it sounds to me like you are loving, interested and involved in your DS's life - he will thrive in your care, whatever the outcome of this proposed further assessment.