You can grow phyllostachys from a segment of rhizome, but it can be iffy...depends on whether you got the right section, the time of year, and whether the rhizome was kept moist. I grow a lot of bamboo and often pot up rhizome segments when I'm taking out runners. Even with immediate transplant, my success rate is probably less than 50% using the choicest, largest section of rhizome, with multiple buds. The success rate also varies depending on which species you're doing.

As for what you bought, the seller was probably quoting the theoretical maximum size for the species. Even if yours shoots, do not expect anything large immediately...that's not how it works. Most of mine that are successfully propagated from even a large piece of rhizome generally only send up a shoot in the 1/4" to 1/2" diameter range. If you were ever to get bamboo several inches in diameter that you started from a piece of rhizome, it would take many years to get there. Most phyllostachys are unlikely to get anywhere close to 4" anyway.

I won't say you were scammed. Just that the seller probably implied a very rosy, unrealistic scenario, and you accepted it.

If you're interested in bamboo, you should start with potted up divisions where you know you have a plant that's already shooting. It's more expensive, but more reliable and gratifying.

From your screen name, it sounds like you may be in the PNW (as am I). What city are you in? I could refer you to some sources that are reliable and reasonably priced.

kudzu9, by any chance originally from back east? i am originally from the south myself and remember the kudzu well. sequim is my homeport. other than bambu-u which i know is near port townsend, i am unfamiliar with the resources around. thanks for any and all advice on the subject.

straitjuanboo-
I'm not from the South, though I've lived there, and I know kudzu can put bamboo to shame regarding invasiveness!

If you know about bambu-u, it would be hard to improve on that for price and quality, especially given your proximity to it. That's where I got started and owe a lot to the owner, Marc Hilt. If you're ever over this way (Eastside), I can recommend Boxhill Farm in Duvall, which has an extensive inventory of bamboo and reasonable prices, too. If you're ever in the Woodinville area, I can usually rustle up a free pot of something for a newbie.

thank you very much for the info kudzu9 and the confirmation on bambu-u. i'm pretty sure i've caught the collector bug and am looking at my 5 acres with new eyes as to where to put the mountain bamboo, where a nice privacy screen might go...etc