Docker: Is there a way I can check if Redis is being used as a cache for PostgreSQL server?

Question

I have a set of docker containers communicating over a network via Docker Compose (one of them is redis and one of them is postgreSQL). I did a Wireshark capture on the communicating containers and I noticed that there's some sort of communication going on with the redis container. The weird thing about this communication is that it is using the PostgreSQL protocol, despite the requests being sent to/received from the redis container. You can see this phenomenon in picture in the link:

In the picture, 172.18.0.4 is the IP address of the redis container, while 172.18.0.5 is the IP address of a different container (not postgreSQL). As you can see, the communication is using the PostgreSQL protocol.

I was told that this is probably because redis is acting as a cache for the postgreSQL server. So I want to look into this a bit more. Is there a way to actually prove/disprove that the redis container is being used as a cache for the postgreSQL server?