Any councillor, or any member of the public, is perfectly entitled to express an opinion on a planning application whether that be before or after a parish / town or county consideration of the application.
Making a public statement of personal opinion is in no way inappropriate.
This is called "predisposition." It is a state of mind which is held at the time the comment is made. It is important to differential between "predisposition" and "predetermination." Predisposition is 'todays' way of looking at it. Tomorrow may bring different thoughts or information to bear which could change the existing thoughts.
If the comment stated - there is nothing that would change my mind - that would be predetermination and demonstrate that the commenter was 'fixed' in their opinion.
It is perfectly reasonable to have an opinion 'today' - which is publicly stated - but could be changed by reasoned argument 'tomorrow' - at a council consideration of the application for example.
So to answer the question - it would depend upon the content of the public comment. Predisposition is perfectly reasonable, predetermination isn't.