Lupin was actually startled when Oko flattened himself too. Wait, what was he doing? Lupin had thought that he was going for the head on approach, and had planned his own strategy accordingly, but now Oko wanted to hide too? That was no good! That meant the enemy would be looking around, which meant they might find Lupin too.
He couldn't afford to be distracted for long though. A moment later, he saw the glint of something sharp in the grass. He had a hunch as to what the enemy Pokemon might be, but on the other hand... Sometimes the best fight was no fight at all. "Run," he hissed to Oko, before darting off to the side at full sprint. That was right, this was a tactical evasion!