Security through obscurity is only problematic if that is the only, or a primary, layer of defense. As an incremental layer of deterrence or delay, it is an absolutely valid tactic. (Note, not commenting on whether that is the rationale here.)

That, and plenty of closed-source software at least has a decent security track record by now. I haven't seen an obvious cause-and-effect of open-source making something more secure. Only the other direction, where insecure closed-source software is kept closed because they know it's Swiss cheese.