I've seen the scientific data suggesting what subliminal messages can do, and there really is no basis to believe it can actually affect a person in any real way. While It's conceivable that a band would hide some reverse-mask messages into a song, your brain, even on a subconscious level, doesn't interpret it. Petra intentionally backmasked a Bible verse into their song Judas' Kiss.
So, my conclusion would be that it's either an intentional "joke" that you could consider harmless, or something completly randomly coincidental. Forms of subliminal advertising that IS real would be to alter the volume slightly on a specific commercial or product, or adjust the lighting in the room to make something particularly appealing. Won't make you act differently, but it can trick you into seeing something as better than it really is.