The term Alloa Ale definitely had a cachet, and was used like Burton Pale Ale or London Porter as a sign of quality. How did Alloa's brewers achieve this? Obviously by brewing good beer, but also by selling it all over the country. In terms of distribution, Alloa and Edinburgh punched well above their weight. Without much of a home market to speak of, Scottish brewers had to seek sales elsewhere.
That explains how a relatively small brewery like Andrew Roy could be famous enough to be mentioned in the same breath as Bass or Allsopp. Admittedly, in the case of the advertisement above, their beer isn't being sold that distantly from Scotland, just in Newcastle. But they did supply London, too.
And Exeter, which is about as far away from Alloa as you can get and still be in the UK: