Was the rig level both times when you checked the oil? If not, that could explain some of the difference.
Either way, I think I would change the oil ASAP. There's really only 2 fluid sources that could increase the oil level; engine coolant or fuel and neither alternative is a good one. If you can't visually see something wrong with the drained oil, I'd send a sample for testing. Blackstone Labs does a good job of testing.
Then on the other hand, maybe it was just overfilled. If it's a Cat engine, they had some problems with inaccurate dipsticks.
Good luck and let us know what you find.
Denny, Connie & Shadow (former barn cat made good)
2000 Itasca Horizon, Cat 3126B, Freightliner Chassis