I don't remember that particular scene, but it was consistent with how the writers were portraying Big Bird at the time.
One incident I DO remember from back then: one time everybody was going to take a trip to the beach, Big Bird included. So Susan and Gordon tell him to get a good night's sleep, they're leaving early the next morning. Big Bird worries if he'll be able to get up the next morning, so he stays up all night rigging his nest with various alarm clocks.
Morning comes, but Big Bird sleeps through all the alarm clocks going off, so they go to the beach without him. Poor Bird. Back then, his heart was in the right place, even if his brain wasn't.