The Gemara begins with an assumption that the two cases of ‘finding’ and ‘all mine’ are one. Based on this, the Gemara learns that even though ‘finding’ could have the connotation of just seeing an object, the extra part of the case, ‘all mine,’ teaches that it is not enough to see an ownerless object for it to be considered yours, rather one must actually pick it up.
Then the Gemara rejects the notion that this is one case and says it is actually two separate cases, one referring to a lost object, and one referring to two people claiming they have bought something.
With this new understanding of the two cases as indeed being separate, do we lose the whole previous thought that taught us that seeing is not enough to acquire? In other words, will it now be enough to look at an object in order to acquire it, being that we don’t have any extra case in the Mishna to teach us otherwise?
So I asked the local Rosh Kollel, R’ Akiva Teichtal, who gives a daily daf shiur, and he said that they asked the same question in the shiur, and they came out as follows. It is clear that the Torah uses the word מצא – ‘finding’ to mean actually picking up. Thus, the Torah itself indicates that there is no acquisition until the object is picked up. At the first stage of the Gemara, all we were saying was that the mishna is coming to teach you this – so you don’t make a mistake – and think that seeing it would be enough for it to be yours. Even without the mishna coming to tell us this, however, seeing would still not constitute an acquisition, thus when we no longer have the extra words from our mishna, we just don’t have the indicator to correct our mistake; but seeing would still not create an acquisition in any event.