To the best of my knowledge, this person was mistaken. They are not in a department that makes lending decisions, nor someone who can make decisions. They have likely had an influx of calls asking about the credit scores shown by default in accounts since they are TransUnion VantageScore 3.0 and the Experian FICO 08 score is harder to find on their website, and it's likely in the script to explain that it's a VS3 score shown.
ALL official Amex channels state that Experian FICO 08 is the one used to manage your account and the American Express My Credit Guide specifically states that it is not the score used by American Express to manage your account.
If American Express were to use VS3 for lending decisions, many people like myself would be in serious trouble. I've had sub-700 VS3 scores while having 800+ FICO 08 scores.
EDIT: I have a letter from a denied CLI request a few months ago that displays my Experian FICO 08 score, although scoring is not the reason for the decline.
I agree, she didn’t say which vantage score they use just that it’s vantage 3.0
American Express MyCredit Guide uses TransUnion VantageScore 3.0, but again I believe you were told incorrect information.
VantageScore Credit Score
The credit score provided through MyCredit Guide is your VantageScore Credit Score. VantageScore Credit Score is calculated by a model (as may be updated from time to time) created by VantageScore Solutions, LLC. VantageScore Credit Score predicts credit risk. Specifically, it measures the probability that a person will pay his or her debts on time. There are many different credit scores in the marketplace based on different models with different scoring ranges. The scores provided through MyCredit Guide are for your education/information purposes only.
Your FICO® Score 8 based on Experian data is the same score used by American Express.