Couchbase server upgraded from community to enterprise edition automatically

I used Couchbase Server Community Edition 6.0.0 via docker and created a single-node cluster. Then created bucket, added needed data, and used it for couple of months via web admin console.

Now when i try to hit the same instance using docker, i get Enterprise Edition page with option to join an existing cluster or setup new cluster. On clicking ‘Join existing cluster’ option and trying to access the web admin page by filling relevant details - it throws error “Attention: Adding nodes to not provisioned nodes is not allowed.”

I want to access the existing cluster from Community edition which i was using earlier; it seems to have auto-upgraded to Enterprise edition 6.0.3 automatically and i am not able to understand the reason.
Can somebody help me solve this and try to understand why it must have happened.

Let know if any more information needed.

Thanks in advance.
Pardon, if some understanding is wrong in above issue stated; i am relatively newer to CB.