It definitely looks like a relatively modern engraving intended to commemorate Buford and his service at Gettysburg.
The choice (and omission) of words shown on the engraving and accompanying display tag suggest (to me) that he did not carry this saber in that particular action, even if it did belong to him. Merely my interpretation, based solely on the word descriptions provided for the displayed item. (I note, however, that Buford's statue monument at Gettysburg depicts him standing wearing a long-blade on his side, but then again, all the Union General monuments at Gettysburg appear to show each of them wearing that same weapon).