Yes,
Perhaps the hitch is mismarked and does not fit a 2001-2005 Sport Trac. It may be for 2002 or later Explorer?? The previous owner may have encounter the same problem and so they sold it?
It's also possible that your bumper slipped when you removed the bolts and now the holes do not align properly?
All the Sport Track hitches I have seen require 3 bolts/nuts on each side, so that's why I think it may not be for a 2001-2005 Sport Trac and the member who sold it may have not been aware of that if they never tried to install it?
...Rich