Sims that walk nearby home lot are added to my Sims relationship panel.

@ProzakJESUS  If mods are installed the first troubleshooting step is to remove them, from the picture so to speak; that is, not guess that they are not causing the issue, but confirm it. How to confirm it:

Make a new folder, and save, and sim, and test to see if the issue occurs.

If it does occur, then the mods are certain not to be involved, since they are not present. Then the explanation is that something is amiss in the game code, and so a bug report for the game can be made/or a work around explanation found.

If it doesn't happen in a fresh save and folder, the next working hypothesis is that the mods could interfere. Then you need to look at what mods you have and ask at the modders forums instead of the offical forum for the, implicitly, unmodded game. This is a player help player site, and not everyone posting here uses mods, or uses the same mods, or in the same combination. Your best bet therefore is to try to speak to the ones knewledgeable in a particular mod, and so you first need to figure out which mod is at fault. 

But for anyone to take  an issue seriously, you must do so first. If you want me to explain it better, just say so.

@ProzakJESUS Hi!  I just had a sim become good friends with Candy Behr, at the discotheque in Windenburg from Get Together, even though they have never interacted with each other.  I saw your post earlier and now I'm wondering if your sim has a good, great or pristine reputation from the Get Famous pack.  I don't know if it was the intention, but just being near a sim with a good or better reputation may generate a friendship, although it seems somewhat random.  There were at least ten other sims at the discotheque and both sims in this household have a pristine reputation but only one got that friendship.  Anyway, I'm wondering if it just might be a bug with the reputation system from GF.

Update: The same sim just gained friendship with two other NPCs even though he didn't interact with them.  Also, the other sim in the household is a 3-star celebrity which may explain why he isn't gaining the friendships.