Seymour 'saw less' than he should have according to his later statements. He said he saw the bolt action and assumed it a Mauser, the de facto standard for bolt-action rifles of that era. The Carcano had a similar appearance, but even if he had only heard rumours about the Carcano bad reputation (let alone knowing it at-a-glance) he would, arguably, assume a Mauser would be used over said Carcano in a Kennedy assassination attempt.