Bua was an All-SEC linebacker. He only played safety his senior year....and went All-SEC again (1st team). If he had decent speed at safety, he has really good speed at LB. Why not let him play a position where he's faster and better suits his aggressive style. Not many guys have the speed or instincts to get away with being Brian Dawkins.
Remember, Brian Urlacher was a safety coming out of college. The Bears moved him to weakside LB. In Week 3(?) they moved him inside, and he absolutely exploded. That's just a best case example. Tommy Hendricks was also a converted safety for the Phins. Corey Jenkins was a QB who played his last two collegiate games at safety. The Phins don't care too much about size at LB. They want speed and instinct.
Remember, Brian Urlacher was a safety coming out of college. The Bears moved him to weakside LB. In Week 3(?) they moved him inside, and he absolutely exploded. That's just a best case example. Tommy Hendricks was also a converted safety for the Phins. Corey Jenkins was a QB who played his last two collegiate games at safety. The Phins don't care too much about size at LB. They want speed and instinct.