That's not what the term means, though, and using the real definition of market share it is impossible to have a negative market share, for the exact same reaso

That's not what the term means, though, and using the real definition of market share it is impossible to have a negative market share, for the exact same reason that you can't have a negative number of people using a product. "Small market share and spectacularly unsuccessful products" is not, even in the loosest possible sense, the same as "negative market share."