Could be "adulterated" honey, or it could be from the raisins. Sometimes raisins are available coated in corn syrup or the like. I've noticed a very greasy like residue after using raisins that had this corn syrup coating. Dunno what else it might've been. If it was indeed due to the raisins having a corn syrup coating, I'd suggest soaking them in water a couple of times until there is no more greasy/oily stuff on them before using. It works pretty well, and then that gunk doesn't wind up in the batch.
As for the batch, so sad that you decided to dump it! Most times you can salvage batches like that with some vigorous champagne yeast. A naturally occurring yeast can be unpredictable, and you did it no favors by starting with such a high gravity must. I realize it was only Sam's Club honey and only a 1 gallon batch, but dumping a batch should really only happen if you know you can't save it. Even then, most mead failures can be used as a unique marinade/cooking wine. Just something to keep in mind for future batches.
Find what you like, and hone it to perfection.
And don't serve dodgy beer!