Maybe someone can help with this

[Cirio]

This rose died off, and the stem on the left grew back and seems to be like the original plant. Then this other growth appeared and seems quite different. Any idea what's going on?

 

[Oliver Buckle]

It was a rose grafted onto a root stock, the vigorous one on the right looks like the root stock, probably a simple briar.
I once had someone ask me to prune a very large old rose that was growing up the side of their house. They came back later in the summer and said it was flowering well, but the flowers only lasted a day, turned out the root stock had taken over completely, grown to about fifteen feet tall and I had pruned it beautifully.

 

[Cirio]

So should I just cut it off entirely? It's not meant to be a climber, just a bush rose near the patio.

 

[Oliver Buckle]

Yes, take the briar off as close to the root as you can get. If it isn't too buried you can probably see the graft and that the rose comes off above it and the rootstock below.

 

[Cirio]

Thanks.
There should be a secateurs smiley here....