The random hobo was the shapeshifter in that example, XD. Sorry to not make that obvious! Older spirits aren't as strong anymore, and it will be harder for them to recover memories because of their prolonged time without a living corporeal body. Spirits wander and bounce off things and the untrained eye wouldn't notice them to be more than maybe a shiver on their arm or a creak in the wood of the deck or something.~
Random phenomena is hilarious and if you can sorta explain it, like say that the guardian heard a news report on such a phenomena, then sure, XDD.
Just remember that any and all vessels must be alive when they are to become vessels! They have to "die" during the process for their body to be of use to the incoming spirit and for the spirits to merge. I realized this when I was going over that cherry question, as it'd be a cherry tree and not the cherry itself that'd have to be the vessel, y'see! A picked cherry is essentially "dead".
-totally distracted by Whose Line again, d'ohhhh-