It could be that your shoulders were more relaxed on that day. I've seen a lot of players hunch up their shoulder so they look like a turtle at address. If you do that you'll have no end of trouble.

If anything I feel my shoulders are pressed downloads a little though they have no stressed tension in them. I also like to feel my arms hang more naturally (verticle) or even pulled in a little. Ben Hogan in his book - 5 lessons (a golf bible) says that the elbows at address should point to their relevent hip bone and the elbow socket should be pointing outwards away from you slightly.

Whatever you do if golf don't try and change too much too soon otherwise your swing will degrade (some aspects of it may be ok anyway) and you'll have a miserable time hitting the ball sideways.

Paul