I think this was copied from Latacora’s cryptographic right answers without some of the necessary context. It’s specifically talking about the KMS offerings from AWS/Google Cloud, which provide trusted hardware implementations of not just key management, but also symmetric/asymmetric encryption, HMAC, etc. All the symmetric constructions provided by these platforms are AEADs, so the point is, if you’re using AWS’s KMS, don’t think about it, just use the default. Which is fairly sensible advice.