"Ethical" in the given examples does not really refer to the quality of the clothing. It refers to how the clothing is produced. In the given phrases, "ethical" roughly means "morally correct". It implies that the clothes are produced in a morally correct manner, as follows.
First consider "unethical clothes" and "unethical fashion". One aspect of this is related to clothing produced in poor region where the workers are treated and paid poorly. The first thing that comes to mind are sweatshops. Of course, this is just a narrow range of issues. There are many more issues surrounding the production of clothing and fashion.
Ethical clothing would the opposite of unethical clothing. One aspect would be clothing that is not produced in these kinds of poor conditions. It would be clothing produced in safe conditions for the workers, where the workers would be paid fairly. Again, this is a narrow scope of the issues.
Below is an excerpt I found on the matter here from the Victoria and Albert Museum with just a few of the examples provided:
Ethical Fashion is an umbrella term to describe ethical fashion design, production, retail, and purchasing. It covers a range of issues such as working conditions, exploitation, fair trade, sustainable production, the environment, and animal welfare.
Some of the issues around Ethical Fashion
Ethical Fashion aims to address the problems it sees with the way the fashion industry currently operates, such as exploitative labour, environmental damage, the use of hazardous chemicals, waste, and animal cruelty.
- Serious concerns are often raised about exploitative working conditions in the factories that make cheap clothes for the high street.
- Child workers, alongside exploited adults, can be subjected to violence and abuse such as forced overtime, as well as cramped and unhygienic surroundings, bad food, and very poor pay. The low cost of clothes on the high street means that less and less money goes to the people who actually make them.
- Cotton provides much of the world's fabric, but growing it uses 22.5% of the world's insecticides and 10% of the world's pesticides, chemicals which can be dangerous for the environment and harmful to the farmers who grow it. (Ethical Fashion Forum)