I mill my grains at the NB store in West Allis (Milwaukee). I do buy my base grain in bulk and bring back what I need for the batch I'm brewing. At that time I purchase the other grains I need and mill them all together. Milling @NB is just too convenient to justify the cost of buying my own mill. There is a downside in that you can't adjust the roller gap. They have them locked in at 0.040". I've never had a problem with getting too fine a crush. In fact I will sometimes run my grist through a second time if it seems too many kernels are not crushed properly. Because their mills are locked down I doubt your crush was so fine that it caused a stuck sparge and overflowed the basket. However, since the grain room is not monitored, it is possible, however unlikely, that someone before you messed with the roller gap and caused your problem.
Not having a grainfather I'm just guessing here but, are there adjustments you can make to alter the sparge water flow rate or some other setting that would alter the process?