Though I agree with you that he might not have carried a gun before, I get different vibes besides the phallic. Say, the perp thinking:
- I might need a gun to do this, but I don't know much about them and I am not a gun guy. Rather, my approach to the gun is its just another tool.
- So, no tacti-cool type militia dude type holsters, no pimped out gangst'ah Glock, just a no frills, no prestige brand .380 pistol in a place that I can get to it. I don't plan on using it, only showing it to an elderly victim to intimidate her.
Maybe the unusual holster is reminiscent of a tradesman used to carrying tools jammed into pockets, in hats, behind ears, tucked into belts, or shirts. The goal is simple practicality, not say a look.