Summary:
We can derive from the פסוק of וגונב מבית האיש that הגונב מן הגנב is פטור from כפל, only according to the מ"ד that it is discussing גנב עצמו, not טוען טענת גנב.
For we learnt; Rabi Akivoh said, etc. - דתניא אמר רבי עקיבא כולי
Summary:
The גמרא asked the question regarding יאוש by גנב וגזלן according to what רבה ורב were discussing respectively, even though there is no logic to differentiate between them. Alternately; the questions were recorded as they were originally posed.