Currently in Mongoid, when an embedded document is saved, the parent is also saved. If an embedded document is touched, the parent therefore would also be touched. It is possible to specify touch:false on an embedded_in association but this has no effect. To provide diagnostics for this incorrect usage, Mongoid should prohibit specifying touch:false on an embedded_in association.
Additionally don't forget to update the docs here: https://docs.mongodb.com/mongoid/7.3/tutorials/mongoid-relations/index.html#touching
https://jira.mongodb.org/browse/MONGOID-5274 is filed as an improvement ticket to implement touch:false behavior for embedded associations.