Calories and sodium are two very different things...
You can have a major deficit in calories - exercise like a demon and gain weight if you go high sodium.
It is like having a bucket on the scales next to you... You are not going to get a similar weighing if the bucket is full of water - even if you have eaten carefully and exercised so that you have burnt a pound of fat.
Be glad that you are a man... A lot of women get water retention around the time of their period too due to hormonal changes... Their weight can be shooting down nicely because they are working hard and then they suddenly see it jump maybe 6 pounds when they havent eaten, drank or exercised any differently at all...
It can be quite demoralising for people if they do not understand what is happening and expect it.
I once had an emergency operation and didnt eat or drink anything for days (rushed into hospital and they knew that they were going to operate so got a "nil by mouth" sign, they even took any food that was en route back using a tube up my nose and a syringe, then after the operation was only allowed "small sips of water" for about a day. When they did allow me some food it was only mushy stuff. Hospital portions are not large and there was no opportunity to have other than I was given. I was ravenous!!
It was in 2008 and I was in the middle of my big project at the time which ran from 2007 to 2009. I was posting on this forum...
http://weight-loss.fitness.com/threads/15690-Omega-s-journey/page128
http://weight-loss.fitness.com/threads/19906-The-Amazing-Race-Challenge-Omega-3-Team/page14
I knew all about how my weight reacted to things... I begged them not to connect a saline drip to me because I knew what to expect. They insisted! I got home and found that between my weighing on the Wednesday and the Saturday I had gained something like 8 pounds... 8 pounds with minimal food...
To be fair I had not done too much exercise in that time - I had been in pain on the Wednesday so had only done my morning walk of over 6 miles...