It must not have been big enough when the quiz was created in 2013. However, as of 2019 it would now be in 19th place, bumping Airdrie down to 20th and knocking Falkirk off this list.
These aren't cities, the cities in Scotland are … Aberdeen, Inverness, Perth, Glasgow , Edinburgh, Stirling and Paisley (not 100 per cent on the last one), but the rest are all large towns. Stirling should be in there for sure.
Paisley isn't a city, but Dundee is, along with the others you mentioned. It does say in the instructions that it includes the largest towns and cities