I puzzled over that one too. Looking up Scots language websites and listening to examples, it does appear these days to be nothing more than English spoken with a Scottish accent and with a few regional words thrown in. Do people in England get asked if they speak, understand, read and write Geordie, Scouse or Cockney rhyming slang? You can't seriously ask a question about Scots without defining or explaining what it is.
I've also had to decide whether my baby and toddler consider themselves to be Scottish or British, or both. I tried asking them but they didn't really understand. Maybe I should have asked in Scots.