It looks like you averaged all of the percentages to come up with 75%. That is not how the scoring works. The different categories are weighted differently. Let's assume the following (I'm making this up... it's not official):
Manage basic networking: 20 Points
Understand and use essential tools: 20 Points
Operate running systems: 40 Points
Configure local storage: 40 Points
Create and configure file systems: 50 Points
Deploy, configure and maintain systems: 40 Points
Manage users and groups: 20 Points
Manage security: 40 Points
Manage containers: 30 Points
Total Available Points: 300
Manage basic networking: 100% - 20 Points
Understand and use essential tools: 67% - 13.4 Points
Operate running systems: 67% - 26.8 Points
Configure local storage: 75% - 30 Points
Create and configure file systems: 75% - 37.5 Point
Deploy, configure and maintain systems: 88% - 35.2 Points
Manage users and groups: 75% - 15 Points
Manage security: 100% - 40 Points
Manage containers: 33% - 9.9 Points
Total Score - 188.2 Points
188.2 / 300 = 63%
So, although you got 100% in networking, I wouldn't see it weighted nearly as heavliy as storage, where you only got 75%.
Hopefully my explanation makes sense.
Again, the theoretical weighted values I posted were only made up for the purposes of explaining how the weighting works. They should in no way be construed as official Red Hat numbers.
Red Hat Certification Central only reports total exam scores to candidates.
Only section scores were reported for exams that consist of more than one section.
I strongly recommend you raise a ticket with the Certification Team if you have any concerns about your exam score.