"Security by Obscurity" is among the most commonly used (sometimes misused) phrase in security industry. The phrase is supported by giving examples like, leaving the back door of your house open, as nobody knows about it or like keeping the key of your house under the door mat or in a flower pot next to the door.
As per wikipedia, the origin of the phrase can be traced back to the Kerckhoff's principle, "a system should be secure because of its design, not because the design is unknown to an adversary".
One such example I can remember is encryption and authentication process in Whatsapp messenger (though in case of encryption, it could be a case of ill-informed cryptographic implementation, but considering it is a well funded company and still lacking on such important aspect, makes me think on lines of "security by obscurity" as well).
As per wikipedia, NIST in its document on "Guide to General Server Security" talks of this security principle. Bruce Schneier in this article talks about it as well. There are many other references on wikipedia like, Peter Swire, Jay Beale etc.
This brings to the important part of the question, does it prove that open source is better than closed source. In my view, it depends on the size of the project, how many developers are working, background of developers, and quality control practiced. There is no way to tell which one is more secure than the other one, just by looking at the model of development used. Historically, both the camps have chequered history.