Indeed, even we
know that Kirk is fallible. In "Obsession", we learn that for the past decade, he has been regretting not being trigger-happy enough. It would be pretty natural for him to have gathered a reputation of always treating a superior enemy to an immediate and ruthless surprise attack and then
opening hailing frequencies.. It would be a small step from that to snapping in face of another "superior enemy", under pressure of the above sort.