Usually operators are defined as being left-associative, right-associative, or non-associative.
So e.g.,
a + b + c is interpreted as (a + b) + c because + is commonly left-associative
whereas
a ^ b ^ c is a ^ (b ^ c)
because languages that support ^ for exponentiation treat it as right associative.
For non-associative operators, parentheses are required if you have two operators at the same precedence, so I believe the grandparent is arguing that e.g. a + b - c should require parens to disbiguate in a language where + and - have the same precedence.
So e.g.,
a + b + c is interpreted as (a + b) + c because + is commonly left-associative
whereas
a ^ b ^ c is a ^ (b ^ c)
because languages that support ^ for exponentiation treat it as right associative.
For non-associative operators, parentheses are required if you have two operators at the same precedence, so I believe the grandparent is arguing that e.g. a + b - c should require parens to disbiguate in a language where + and - have the same precedence.