The TA writes down everything (s)he sees no matter how important it is and doesn't give any "point". The actual grade is computed from the list of issues collected from the comments.
The issues are not specific to the subject rather they are generic comments that can be made about any piece of C code. The issues are codified using a universal issue list. There is little to no room left for interpretation. A direct consequence is that the grading must be as fair* as possible.
* Fairness here means that the handouts should end up sorted by subjective quality based. There is still a subjectiveness bias but it applies to all handouts equally and is not dependent on which TA graded it.