A “possibility?” Of course. A likely possibility? No.
Well, disagreements over what that probability might be is essentially the heart of discussions such as these. I would say I assign it a higher probability than you do, but I wouldn't go so far as to say it is a likely possibility. Only that I give the probability of ghosts existing a considerably higher value since that experience than I did before that experience.
Is it fair to say that you lean in that direction? Or that you think the ghost explanation is as likely as any other?
Hmmm. I don't lean in any particular direction as much as I am puzzled by the experience, it fits that general description and I have no other explanation (rational or not) that fits.
This is a perfectly reasonable position. If you want to carry it further, you can choose two courses:
1) Seek an explanation through researching the literature and visiting forums such as this one.
Unfortunately, the general level of discourse in this forum when people attempt to discuss such experiences is so acrimonious, that I prefer not to. I haven't wanted to discuss the experience in detail here because many posters grow irate when someone refuses to accept explanations such as pareidolia or misremembering as sufficient. Accusations of lying are not uncommon either. I mentioned it in this thread only because had some similarities to experience Sir Phillip described and thus lends some credence to such experiences as being legitimate real occurrences, not just misrememberings, hallucinations or pareidolia.
Those people I have discussed it with (not here) fall into one of two camps -
1. It's definitely the spirit of your dear departed friend, why do you doubt it?
2. It's definitely not a ghost because ghosts don't exist. I have faith there is some rational explation for what you saw even if I don't know what it is.
There is a third camp, but I avoid discussing it with people who fall into this camp.
3. I'm a liar or experiencing pareidolia, misremembering, or hallucination.
I know I'm not lying. I see no reason to think that I have misremembering the experience as I journaled the experience soon afterwards. Pareidolia seems unlikely since I saw no form or pattern, just a white cloud. There is no reason to presume I had a hallucination. I wasn't on drugs or dreaming.
2) Seek an explanation using only your own knowledge. This is what it appears you are doing. This leads to the old argument from ignorance thing and the Ghost of the Gaps explanation.
I never heard the ghost of the gaps explanation before.

Cute. I have, in fact, discussed it with others (not here) and tried to find other rational explanations. There are none that I am aware of.