It shouldn’t be – probably Duolingo treated it as a typo (because it’s only one letter difference), and recently it seems Duolingo doesn’t even report typos, just accepts your answer. Unfortunately Scottish Gaelic course contributors cannot do anything about it – that’s a problem with the Duolingo software.
Too bad. Software & the internet are amazing and make things fast but also can be fast at the wrong things. It bothered me that Google translated "foileag" as seagull so I filed a bug report. We eat a lot of pancag, crampag and pancakes around here but no seagull, guga, nor sgadan.