"products made by one brand" isn't a category of products. If they're the only brand that makes products for a particular category, then they're a monopoly, but you cannot simply define a category as "stuff made by that company", because by that logic, every company is a monopoly on stuff made by them.
Actually, a makers own products are a distinct market for antitrust purposes if people empirically don't substitute out of it, as shown by the producer having market (pricing) power.
I wouldn't be surprised if that's true for Apple for some of its offerings.
It's not. The only product you could even try to make the argument for is the iPhone, but the generally-accepted categorization here is that iPhone and Android phones (and Windows phones) are part of the same category, which makes sense because people absolutely do switch between them.
Actually I have a better argument against this than my other.
No, "products from brand A" is never a category. However, a company may create a brand new market with a product, and they may be the only company with a product in that market for a while. But that still doesn't mean the category is "products by that company", it just means it's whatever new category was created from the product.
For example, the iPhone arguably created a new category of smartphones. But competitors quickly introduced their own products in this same category (e.g. Android).
