Our default relationship from WORKORDER to DOCLINKS has this:
select doclinksid from doclinks where (ownertable='ASSET' and ownerid in (select assetuid from asset where assetnum=:assetnum and siteid=:siteid))
That should only surface attachments that are directly referenced on the asset. I would expect the asset to show the same but if I'm reading your message correctly, you have confirmed that it does NOT show these attachments on the Asset. It's possible someone has modified the DOCLINKS relationship between WORKORDER and DOCLINKS so that would need to be reviewed. You would have to check that in Database Configuration.
It's also possible someone in the system settings (managed inside the Organization application) has enabled "Create asset doclinks at system level". What this does is it causes us to use a different relationship (DOCLINKS_ASSETID) to show the same attachments even as assets get moved between sites. We use the ASSETID field on the ASSET in this situation which could correspond to multiple records in the database.
ownertable='ASSET' and ownerid in (select assetid from asset where assetnum=:assetnum and siteid=:siteid)