This question might be larger than just on the Bartenura, but it was a passage in his commentary on the Mishna that inspired it:
In Menachot 8:7, the mishna states that the Temple treasurer would watch the pouring of wine for libations in order to check that there was neither froth nor sediment in it, and that he would strike with his stick (perhaps against the side of the barrel) once it was time to stop pouring. The Bartenura comments on this, suggesting that the reason that he used a stick rather than his voice is that speech is harmful to wine (לפי שהדבור קשה ליין).
He credits this idea to his teachers (...ורבותי פירשו), but also acknowledges that it's found in the gemara (והכי מפרש בגמרא...). In fact, it appears in the gemara almost exactly as the Bartenura transcribed it:
אמר רבי יוחנן כשם שהדיבור יפה לבשמים כך דיבור רע ליין
Rabbi Yohanan said: Just as speech is good for [the grinding of] herbs, so is speech harmful to [the pouring of] wine.
- Menachot 87a (≈ Keritot 6b)
My question is: if the gemara provides this explanation explicitly, why did the Bartenura credit it to his teachers? And if the point was merely to show honour to his own rabbonim, why would one ever credit something to the gemara if they heard it from their teacher first?