Sometimes when ordering roses, the rose company inadvertently sends the wrong rose. Out of all of my rose on-line ordering (which is pretty much every rose I have), that had happened to me only once. I contacted the seller and showed them the picture. They agreed and sent me the right one at no charge.
If you are asking about why DA roses may have different habits in your yard as opposed to where they were originally bred, that is a whole different topic. You don't state where you are located, so I will just go on my own personal experience with DA roses. Where I live, it is WARM/HOT. Where David Austin lives---not so much! Many of his roses that were bred in England, once they get to a warmer climate with more sun, they really take off. For example, David states that his Princess Alexandra of Kent stays small and can be grown in a pot. Maybe in England, but not here in my yard! First year, on own root she grew to be over 8 feet tall! It is interesting that now that I have moved her to a different location in my yard where she gets all day, hot sun and can spread to her heart's content, she is not getting above 3 feet! Poor thing. I feel for her. She is not liking where she is growing, yet at this time, it is the only place where I can put her.
So to answer your question (hopefully), everyone's growing environment is different and roses will respond accordingly. Austin's are pretty notorious for getting much bigger in the US than in the UK due to our growing conditions. There is nothing wrong with the rose. It is just that the breeder has much different weather conditions in the UK than here in the US, so the plants act differently. How my plants do in my zone where I live, will be very different, than plants in zone 6 or zone 4. Seeing what you get and what you can grow and where you can grow it is half the fun! However, in my small yard, I am now leaning towards roses from breeders with similar growing conditions like mine. I know those roses will do well in my climate.
