It's not a notification. It's an OTP/Authorisation request. Did you read the article?
The scenario you give (in bold) is a LOT more likely to happen with a sim swap or your email account being compromised.
From the article:
“If the customer does not have the FNB App or does not respond to the FNB App push message to approve their online purchase, they will receive the OTP via SMS, App messaging and by logging onto Online Banking messaging,” FNB said.
“Receiving OTP via email is being discontinued in line with the bank’s strategy to discontinue communication via this format for safety measures.”
So, even so, it still gives the SMS OTP which hopefully will go away soon.