Using root account in elb S3 policy

Hi, In the documentation to enable ELB logs, it is stated that I should add the following policy to my S3 bucket :

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::elb-account-id:root"
      },
      "Action": "s3:PutObject",
      "Resource": "arn:aws:s3:::bucket-name/prefix/AWSLogs/aws-account-id/*"
    }
  ]
}

I'm a bit confused by the "Principal" field. It seems to allow the root user of a global elb account. Who does this policy actually allow to access the bucket ? Does that mean anyone can send their elb logs to my bucket provided they know the arn ? Or is it only for my aws account ?