google knows if you found what you're looking for because they observe your behaviour. If you keep going through to page 30, it means your search was unsuccessful. if you search again for a similar term ten seconds later, it means your search was unsuccessful. they don't need to ask.

but in this case, it probably just means that people were using it like "cookies+cream". they aren't using + as an operator, they're using it as a synonym for "and", and they are better served by google parsing their query as native language instead of parsing it as an expression in a rarely used query language.