Well, if that's oil from replacing the oil filter, who's doing the oil changes and not wiping things down after they get the new oil filter installed? It always pours onto the front diff and other areas so I wipe things down with a rag afterward. If it's the OP, Dude wipe it down after you get done so you know when you see oil under your rig it's an actual leak. If it's a shop doing oil changes for you, I suggest you chose another shop because that's sloppy work.
I'd clean everything really well and then keep an eye on it to see if more oil collects again. Then you'll know you for sure you have a leak.