I suspect that the interest was earned while the money was outside of an IRA during a rollover. I did such a rollover many years ago myself. That was before the IRS began treated all of ones IRAs together for the purpose of the one-rollover per 12-months rule. These days I wouldn't consider doing a distribution and rollover unless absolutely had to. I now move IRAs by trustee-to-trustee transfer. With a trustee-to-trustee transfer the funds are never treated as being outside of an IRA, so there is no potential to earn interest outside of the IRA.
