>>23496592
Gyunei got surprised earlier in the Keyra hostage scene. He demanded Amuro drop all his weapons, so Amuro ejected his funnels but Gyunei thought they were radiator plates and completely discounted them as a threat, only finding out that they were actually the fin funnel weapons moments later.
In the later fight scene, Amuro drops a bunch of gear right in Gyunei's line of sight and Gyunei is apparently paranoid, he locks his eyes on them expecting them to be like the funnels from earlier, I guess maybe he was trying to be prepared since funnels are generally a pretty dangerous weapon, after all they're small weapons where if you lose sight of them, they can zip around and attack you from unexpected angles.
But it turned out to be just the shield and bazooka floating harmlessly on their own, and Gyunei focusing on them gave Amuro a split second chance he needed to zip around and line up a lethal shot on Gyunei while his attention was away from the Nu.