When it comes to the final fantasy series, almost all bosses have a set attack pattern. The easier ones, you can simply ignore it, but with the harder ones, it helps to learn the attack pattern to know what to defend against. Shrimpy simply does not want to put any effort in this, and is simply walking into a brick wall while ignoring the open door on his right.
Due to his years of playing warcrack, he should know that many bosses come in two flavors: tank n spank and bosses with mechanics. So this first boss was most likely designed to get him used to dealing with bosses that have certain mechanics to the fight.