Is it giant reed grass? Photo below.

Here is a link that might be useful: Arundo donax

Hi Buyorsell888,

Thanks for the idea. No, I believe a giant reed grass is in a grass family just like bamboos. The plant I saw is definitely not a grass. The shape of the leaves is more oval and the stem doesn't have nodes and internodes like plants from the grass family. Although, this plant has stems that are hollow (I think).

Leycesteria can look a bit like bamboo.

Here is a link that might be useful: click on number 6

the middle picture shows the shape of the shrub's branches and stems well.

Here is a link that might be useful: another leycesteria pic

Thanks Plantknitter, the description is very close but two characters are different. The plant I saw is less bushy, most leaves appear on top so most stems are exposed. Leycesteria's leaf has an elongate tip (?) but the plant I saw doesn't have it. The leaf is more oval.
But Leycesteria looks very interesting. I might just get the gold leaf one:-)

Sounds like some sort of knotweed, Polygonum species (although taxonomically confusing....also includes Persicaria, Fallopia and a few others). Many of these are rampantly rhizomatous and/or invasive. Some of the very weedy ones tend to form long hollow stems and have leaf growth clustered at the top of the stems. And can also produce large oval, almost heart-shaped leaves. They grow in colonies, much like bamboo, and are even referred to by the common name of Mexican bamboo (who knows why - not Mexican and not a bamboo!).

With very few exceptions, not something I'd recommend planting intentionally :-)

Yes, one of the weedy knotweed species is almost certainly what you saw. The most common one here is Bohemian knotweed. This is often mistaken for Japanese knotweed.

Here is a link that might be useful: Class B Noxious Weed Bohemian Knotweed Polygonum bohemicum

Thank you all for the suggestions. I looked at the pictures from the links and I still don't think the plant I saw is any of these. Maybe the guy trim it. I should go back there and take a good look/photo:-)

If it pertains, at this time of the year knotweed stems likely to be still in process of growing up and unfolding leaves.

But the stems look jointed, hence "bamboo".

If you went back and took a good picture, posted it here that would probably lay the matter to rest.