Actually, looking at the two, have you been buying upgrade nodes on your characters? If so, then this applies to your fight score. Even as a gold, bronze characters will have "okay" fighter score, maybe even more than your silver one now of course (as all golds "do"), but if I'm correct, after buying enough nodes for your silver Beowulf, he should be at his prime!
That said, because it is a gold card, this means your bronze Beowulf, even if you bought all the upgrade nodes, will have a higher Fighter Score than your silver one until you go ahead and pump that other Beowulf up too!
And a key reminder: While all fighters can be turned to gold with the right materials and things needed, bronze "gold" characters will always be weaker to silver "gold" characters. Gold characters on the fly will be the most powerful overall! Therefore, it's why your gold beowulf, even though he was originally bronze, has a higher fight score than your silver one, you just upgraded him more!