Boss
Take a Memo:
The Science Dictionary says:
ZYGOTE :
A zygote is a fertilized egg containing two sets of chromosomes, one from the egg (oocyte) and one from the sperm. The zygote is a single cell and the result of a fusion between two gametes, an egg (female) and one sperm cell (male).
Go argue with them. Tell them they've made a mistake.
I understand what the science dictionary says but it is designed for intelligent people who understand communicative context. You'll notice there is no period at the end of what you bolded. If the dictionary said "zygote is a fertilized egg." then you'e be correct, but it doesn't have a period there because the sentence continues. The diploid cell produced by the fusing of egg cell and sperm cell is no longer an egg cell. This is why we use a different word (zygote) to describe it.
You are trying to pretend the zygote is still just an egg cell which is now "fertilized" but fertilization can only be confirmed if it successfully results in reproduction. If reproduction happens there is a living organism.