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It could certainly be a sucker coming from under the graft point.Unfortunately, your photos did not come through, so I am unable to see the trees in question. There could be a chance that another plant is growing from the base, as well. I'd have to see it to get an idea of what is going on.

Regardless, you should remove them as they appear. They will sap nutrients from your tree.

https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-sucker-removal-and-tree-sucker-control.htm

With a search, you can find this article that will go into more detail about the two types.

https://www.gardeningknowhow.com/ornamental/foliage/bamboo/common-bamboo-varieties.htm

The article that you read happens to be for invasive bamboo. However, if someone doesn't know the difference, then many people will make the mistake of planting one that is highly invasive in their area. Many people see one thing, then will cease research for other information. For that reason, we have to warn people of the invasive nature of the most common bamboo.

Keep in mind that in some areas it is illegal to plant invasive bamboo, like Massachusetts, New York, Connecticut, and New Jersey, carrying heavy penalties and fines. Mistaking running as clumping may result in more trouble than one wants.

Likely, it is a Phyllostachys. Maybe P. aurea. These are typically much hardier than tropical Bambusa species. They should be fully hardy in your area, but you can take measures, such as mulching, to be sure that it survives. You can try and ask who you got it from about which it is. That would get you a more accurate answer.

You might try and take samples you your local extension service. They would be able to test and give a positive ID.

https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm