Hi,
The document you are referring to is discussing Azure Virtual Machines and Cloud Services. Not Azure WebApps.
https://docs.microsoft.com/en-gb/azure/cloud-services/cloud-services-choose-me

For Azure Web App it is technically running on an Azure Virtual Machine. Those machines all have the correct anti-malware and anti-virus software installed and running to protect itself.

you can check the below documentation on securing PaaS deployments such as Web Apps
Securing PaaS Deployments
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