VKSpotter works out bearings and distances in the following way:

• If the station you spotted is not a member of VKSpotter, then it will use the center of the grid square you supplied.
• The same is true if they are a member, but you supplied a grid square that is different to the one supplied by the member.
• If the station you spotted is a member of VKSpotter and they have not set a latitude and Longitude, it will use the center of the grid square supplied by the member or the one you supplied if it is different.
• If the station you spotted has set a latitude and longitude all bearings and distances will be calculated from that, unless the grid you spotted is different to the one supplied by the member.

Simple really

So the answer to the question is: The DX station is a member and you supplied the same grid square as they have set, but they have set their latitude and longitude incorrectly.

Now go tell them nicely how to change their Lat Long.