Contractors typically buy their paint where they have an account, and/or get the best discount.

If the color is off, have them make it correct.

When a painter quotes on a job and supplies the paint, they normally use a paint where they can purchase for less, if there is no discussion on a brand and quality level. In your instance, BM was stipulated, so I would be looking into why and also discussing that you don't like the paint color and come to a resolution on how to resolve. The quality levels within a brand make comparing brands difficult, in regards to that question.

there is no reason that SW couldnt have color matched a BM color.

when i'm hiring a painter i specify a color but not a brand. even though i always use BM paints myself, i give the painter the luxury of using what they like; otherwise they endlessly complain about the brand you make them use and blame any faults of their own technique on the paint.

but that is no excuse for not having the colors match expectation.