I agree that Data's defacto lie by omission does show growth in Data's original programming, but I don't think it necessarily indicates he has emotion. Nor does him firing on Fajo indicate malice or emotional response. In fact, I would say that everything he did in Most Toys was a logical response, and likely given the facts he had at the moment, the only response.
We know Data was originally programmed not to kill, but that was prior to him having life experience, and encountering situations where the "no kill" program came into conflict with other programs (IE protect life). For example, after Tasha is killed, Data straight up says to Armus that he should be destroyed. I would argue that when Data pulled the trigger on Fajo, at that time, he didn't know when or if he would be rescued. Data reasoned that Fajo was a cold blooded killer, that if Data did nothing, might escape and kill again. SO, like Armus, he came to a logical conclusion that Fajo needed to be destroyed. Note that logic doesn't always mean moral! Also, it does indicate Data has grown past his original programing, to not kill. In this circumstance, his life experience told him that there are cases where he must over ride his "no kill" programming for what is (or seemed to him) the greater good. In this case, Data was reasoning Fajo could kill again, and needed to be destroyed to prevent that. This isn't all that different than examples of other officers bending the rules with the Prime Directive.
As to his lie by omission, I agree he did it. But again, I think this doesn't necessarily indicate emotion. I think it was more about logically preventing Riker from asking the follow up questions of "Did you fire," and "Were you trying to kill Fajo," which I think Riker actually knew the answer to the questions, so Riker didn't ask. Also, Data knows if he admits to attempting to kill Fajo, this could hurt the chances for prosecuting Fajo. So he does the logical (again, not necessarily the moral) thing to say as little as possible. Fortunate for Data, Riker must have reasoned that since Data fired, there must have been a good reason, and therefore he shouldn't ask any follow up questions. This is again an example that Data has gone beyond his programming, but doesn't necessarily indicate emotion.