The underside of the horn boasts an emblazoned seal with a hammer and lightning bolt. Something about the horn seems extremely out of place on a Magnataur.
Take the horn south down the Path of the Titans to Wyrmrest and seek out someone who might be interested in these threatening implications.
It is indeed strange for any magnataur to carry an item such as this... and very concerning. I am glad that you have shown this to me.