Exactly. Not to mention that "boomer" predates the baby boomers by a few decades. It was used for people in the boom towns during the gold rush.

It's an insult, so it's a metaphor. When you call someone a bitch, you're not calling them a female dog. When you call someone a bastard you're not accusing them of being born out of wedlock.

You're calling them the negative things associated with the noun.