The Mishna on Ketuvot 75a starts with a lengthy quote of Rabbi Meir, but the Gemara on 75b ignores that this Mishna is attributed to Rabbi Meir and asks is it the Mishna of Rabbi Yehoshua or of Rabban Gamliel!
I thought of saying that the Gemara is investigating the statement of Rabbi Meir, to find out with whom of the two Tannaim of the previous generation - Rabbi Yehoshua or Rabban Gamliel - Rabbi Meir concurrs, but I had to drop that explanation, because of the statement of Rabbi Elazar:"Tavra! Mi shashana zo lo shana zo" - one must attribute the beginning of our Mishna to one Tana, and the continuation to another.
Could it be that the Gemara did not have - in the text of their Mishna - the words " Divrei Rabbi Meir"?
However - from the start of the words of Rava "Reish Kan Nimtze'u" etc. it may be possible to say that both Rava and Abaye know that the Mishna is attributed to one Tana - Rabbi Meir, and this possibility is supported by the Gemara on the following page (76a) where Rav Avia question Rav Ashi from the Tosefta which quotes Rabbi Meir, and Rav Ashi doesn't answer saying that the Mishna is attributed to Rabban Gamliel!
Nevertheless - Rashi continues to explain the Gemara as if the Mishna does not have the words " Divrei Rabbi Meir".
Could it be that the Rashi also did not have - in the text of his Mishna - the words " Divrei Rabbi Meir"?
As you thought, the Gemara wants to see according to whose Shitah the Mishnah is written, not who is the actual author. As for Divrei Rebbi Meir, there is no indication that it is going on the Reisha where there is no Machlokes between Rebbi Meir and the Chachamim, and therefore the Reisha is written Stam.
Dov Zupnik