Well both terms are unfortunate, but yeah basically just slang for the seeds that you find in shit weed. I don’t ever use the terms though, I just use “reggie” (meaning “regular weed”) for cheap weed and “seeds” for… seeds. Lol. As to why people started calling them beaners and "n****r weed is anybody’s guess. I’m sure the answer’s relatively easy to find but it doesn’t particularly interest me and I’ve actually only seen it online, nobody I’ve ever dealt with in person has said that to me.
I grew up in the 80’s so I can understand why you haven’t heard it personally. I always referred to it as “dirt” weed because it was crappy, bottom of the barrel quality, weed.
I haven’t smoked in forever and I’m okay with that but I do remember using quite a few terms that I don’t see used anymore. We never called it “reggie” or “n****r” weed, ever. Those are terms that are new to me.