He notices from a glance it fits him. Only when he is using the armor. The Spartan looks at Ami as he holds the sweater in his hands, wordlessly asking her if this was a prank of hers.

Even then, he still tucks the clothes in the carriage compartments of his armor. It could still be used.

And it was Ami's gift. He remains in silence for a while as he does so, but not removing any distance between himself and her.