The only time you have to say something is a feature, not a bug, is when it appears to be a flaw. The notion behind this idea is that there was an intention. That aspect of a software, or product design, or service experience was not supposed to be a flaw but an intentional part of the design. It assumes there was an intention, some objective being served.
The reason people might think it was a bug could be because:
- They had different objectives from that of the way the product designer had imagined the objectives of their users to be
- They were not the target audience of the product/service
- They were forcefully making a product fit their needs
- They did not know how to use the product – which could reflect badly on the UI design or the UI of whatever instructions needed
- The product had a poor product-market fit
- The product designers were giving excuses for themselves
There isn’t supposed to be a debate whether something is a feature or a bug. It should always be resolved by the one who had designed the product/service. If it was a result of something being overlooked, it is a bug, and pointing out that it could be a feature is just an excuse.