On daf 127a, the Gemora says Kashya, and Rashbam points out the the Gemoro did not say Teyuvta (my understanding is that he is saying that the proof is not 100% conclusive).
However, we learnt on 52b that the Rashbam does not believe in a difference in meaning between Kashya and Teyuvta (DH Kashya), rather that the difference depends on how the proof is brought!?
Can you shed any light please?
According to the rule the Rashbam writes on 52b this question should have been a Teyuvta, because it is from a Mishnah. That is why he is forced to say that the Gemara wrote Kashya (rather than Teyuvta) since the proof is inconclusive. (See NODA B'YEHUDAH Mahadura Tinyana, YD 163, cited in Insights to the Daf.)
Yes that is correct.