مَا أَثْبَتُّ النِّسْبَةَ، بَلْ ذَكَرْتُ أَنَّهَا مَحْتَمَلَةٌ.
I did not establish the attribution; rather, I mentioned that it was possible.
Mā rejects the claim wrongly imputed to the researcher, while bal redirects attention to the actual, qualified assertion. This is especially useful when the colleague has confused reporting a possibility with declaring proof.
Merely stating al-nisbatu muḥtamalatun may not explicitly cancel the earlier misunderstanding. Negation followed by correction clears the false premise and establishes the intended position. That does not mean every such construction must be assigned to one fixed technical subtype of qasr without considering context.