Why they didn't state that on the death certificate, who knows?
It's likely to be due to the death being sudden or unexplained, or where the person had not been seen by a doctor prior to death. In Scotland such deaths are reported to the Procurator Fiscal who will then instruct the necessary enquiries to establish the cause of death and arrange a death certificate to be issued. The entry on the Registration of Corrected Entries will state that the PF has authorised the identified cause of death to be recorded.
The Crown Office and Procurator Fiscal Service provides some additional information:
https://www.copfs.gov.uk/investigating-deaths/our-role-in-investigating-deaths"When a person dies in Scotland, they cannot be buried or cremated until a medical certificate giving the cause of death has been issued. This certificate must be completed by a doctor, and must show the time, place and cause of death. Most sudden and unexplained deaths are reported to the Procurator Fiscal because a doctor is unable to confirm the cause of the death and is therefore unable to issue a death certificate.
Once a death has been reported to the Procurator Fiscal, the Procurator Fiscal has legal responsibility for the deceased's body, usually until a death certificate is written by a doctor and given to the nearest relative."
I've seen RCEs for deaths as the result of accidents, for folk collapsing in the street, as well as my own great great grandfather who died sitting quietly in the backroom of a pub.
Best wishes
Rockford