Smoking After Fat Transfer to Penis

any time a graft is done, whether a skin graft or fat graft, smoking is known to be a detriment as it may interfere with oxygenation of the new cells which is needed until they develop their own blood supply. I do not think that smoking would contribute to scrotal swelling in your case but there may be a lot of swelling in the scrotum after penile fat injections in non-smokers.

Nicotine is a drug that causes vasoconstriction.  That means it prevents optimal blood supply to the fat cells that require nutrition, glucose, oxygen, etc.  Thus it can significantly affect your outcome nad fat survival.  In terms of fat cell migration, it is unlikely to have any relationship to the smoking.

Cigarette smoke contains hundreds of toxins in addition to nicotine. The overall effect of smoke is a narrowing to an obliteration of blood flow in skin and especially in the skin of extremities (which includes the digits, ears, nose and penis).
I am not going to question the logic underlying fat grafting of the penis to increase width. The operation has multiple complications and as a result is not done by most surgeons. Using different implants in this location has been equally disappointing. The skin of the penis is very thin and the subcutaneous plane is not very well vascularized. As such a lot of the fat dies often forming scar nodules but sometimes extruding and draining. With this in mind, you should do everything in your power to MAXIMIZE circulation in this area NOT hamper it by smoking. I would greatly advise you to quit smoking for as long as possible to maximize graft take.
Living fat cells stay put. They have their own blood and nerve supply and do not migrate. On the other hand, blood and other fluid will drain to the scrotum. The fluid you may see is blood from the grafting procedure.