Yeah, I noticed this too.. I think ur right about it being edited for release.. seeing how the rest of the song is clean.
But then again, maybe Pac just mouthed "in this muthafucka" because he was drunk. U can see him sippin on liquor the whole time and it was pretty obvious that he was buzzin. We all know that if he were to say, "U know LA up in this..." he probably woulda said "Muthafucka," especially when drunk.
Thinking about it logically, had he said "Muthafucka" during the recording of the song, they easily could've kept it on there, seeing how the rest of All Eyez On Me had a lot of profanity.
At the same time, "California Love" was the lead single and we've seen the lead single being kept clean on the retail album even though the rest is still explicit (ie. DMX's "Slippin"). So, we may never know. All we know is that out of all the released versions of "California Love" (and there are quite a few), none of them have Pac sayin "muthafucka" at that point in the song.
Peace.