That's right, and it's actually the recommended way in the XEP: https://xmpp.org/extensions/xep-0277.html#post_comments.
[plugin pubsub] Building the node identifier for the commentscreated
The identifier of the node to store the comments is build like that: urn:xmpp:comments:_<random UUID>__urn:xmpp:groupblog:<publisher> Why don't we use instead of a random UUID the main item identifier to which the comments are associated? This is also a UUID. Doing that will allow to guess the main item identifier just looking at the comment node identifier and vice versa.
This is fixed in rev 4c4f88d7b156