I know a lot of practices use MedTech32, but don't think they can access one another's information unless its been requested for them to share.
Medtech or not, most practices (doctors) have the ability to send (on request) appointment notes or complete history to another practice. Mr XPD may be well aware of Health link and/or RSD/GP2GP.
This would normally be done if you need to see another practice (urgent care of some style maybe) and they may ask if you want your notes from that appointment sent to your normal GP Or if you wish to change doctors your medical history can be transferred "as a whole"
While Doctors have the ability to request services from their respective DHB for a patient, there is no way of the DHB reaching into the local GP's system and accessing a given patients records.
The bulk of the online personal record management systems (MMH, Connectmed etc) are private companies who are working with the various GP's software to provide people access to their records.
Each DHB will have any info of you if you have been seen at a hospital in their area, There are ways of DHB's sharing information, but again its a request/logged etc.
While it should not be done and if it is its against the law etc, are you suggesting your worried this person might access your records to somehow gain advantage based on record notes in your dispute ?