Most likely it may be an error and/or a lag between servers uploading the complete statistics for said day. Were your impressions the same? I would assume that if it wasn't a what I stated above then your impressions would be down tremendousley.
With that being said, unless it drops off 90% or more and stays like that for 7 straight days then I wouldn't worry about it and continue doing what your doing.
Traffic will always be up and down. Some day it'll be down 100% from the previous and others it won't and we can't blame eBay for that since they can't control peoples computers and search/purchase for them.
For example my traffic is down 23.1%(impressions), 13.1%(page views) from last month but my sales are still normal and trending upward this month. If it was down 80% or more for the whole month then I'd know that I am most likely doing something wrong.
