Got regional data transfer usage between Lightsail and EC2 within the same region

Hi:

I'm using VPC peering to connect my EC2 and Lightsail instance within the same region and AZ. The EC2 has no public IP address, but from the usage report, I found the EC2 somehow has regional data transfer usage with public IP. VPC log also shows no transfer to anywhere outside of the AZ, is there any possibility that some other AWS service could cause this issue? Thanks.