I don't see a problem with considering salsa as vegetables, since it is usually just vegetables and spices. Ketchup, on the other hand, usually has lots of added sugar. And your point stands, people do eat salsa in significant quantities, unlike ketchup.
Quantities aside, there's a logical flaw in Brian-M's argument, as he's attempting to say that because there are gradients, there can't be a distinction between the endpoints.
The fallacy has different names; wikipedia calls it [
Continuum Fallacy]
"You can't say in what processing step ketchup stopped being tomatoes, therefore ketchup is a vegetable."
"You can't say in what processing step corn syrup stopped being corn, therefore corn syrup is a vegetable."
"You can't say what day my grandmother stopped being a baby, therefore my 99 year old grandmother is a baby."
Common sense alone should tell us this argument format is invalid, but it finds a happy home in skeptic forums.
What's missing is that the categories have many factors, and there's a "point" to the categorization. In the case of dietary guidelines, vegetables are recommended due to their health benefits. At some point on the manufacturing journey, ketchup stopped having those health benefits (removal of insoluble fiber and water mass, addition of sugar, basically inverting the nutritent/calorie ratio that makes vegetables a better health choice).
Since the purpose of the legislation was allegedly to shape healthier dietary choices, ignoring the impact of processing was abandoning the stated goal. It was a sellout to industry lobbying.