...so what?
What story or original property do you positively NEED to use this specific proto-tweety? Who'd even recognize it was this bird in specific? Why would it matter? Even if it wasn't public domain, Who'd stop you from using a practically identical distinct bird?
Fun Fact: You, yes, YOU, own this character apparently. "A Tale of Two Kitties" is in the public domain, and thus this early version of Tweety (named Orson) is as well, but only from this cartoon.