Any possible assortment of things could have done that. Setting something on top of the spring could even cause it, but no problem. IF you feel that it is too tight, just adjust it slightly to get the tension you want. The same if it is too loose, just tighten it up a little. To adjust it a little looser, just lift the spring until you get what you want (a little at a time) and to tighten it up a little, slightly bend it downward until you get what you want (again a little at a time).

Hope this helps.