You did not receive a downvote.
Rather, six points were lost from either
a) the removal of an upvote (doesn't count as a downvote)
b) your answer was un-BA'd
Qwerty_Zoom has an easier way of saying what I'm trying to.
>It's probably the removal of an upvote because you lost 10 points because of it, and subsequently gained 4 (Ba'd two answers, for 2 points each). That gives an exact -6.
908 - 10 = 898
898 + 4 = 902