In years living in Japan, I heard 会社 used for someone's personal office... never. オフィス or 教室 or 事務所 sure, many times, but never "company". Although I or a native Japanese speaker could understand it as a natural semantic extension. As a lesson for a beginner student, it is very wrong.
Can only agree. I lived in Japan for several months to learn Japanese and they used 事務室 for the office (literally the "office room") in our language department. The overhead department in charge of the whole exchange program was the official 事務所。If I ask a friend どの会社に勤めっていますか？, what 会社 they are working for, I will always get the name of a company, never "public relations office" or stuff like that. This is simply wrong and needs to be fixed.
This is one of those little quirks that Duolingo introduced without explaining what it does. When a small character is present, it alters the pronunciation of the character before it. In this case the character before it, "shi" becomes "sha" when the small "ya" character comes after.
In other words… しや — where both characters are the same size is "shiya". But しゃ — where the "ya" is smaller becomes "sha".
Personally, I've had a little bit of a hard time differentiating between the regular size hirigana and the smaller characters, so I often miss these the first time around.
The other two characters that I know of (so far) that become small and change the pronunciation like that are "yu" and "yo", ゆ and よ.
So, in addition to しゃ, there's also しゅ and しょ — "shu" and "sho", respectively. There's a full list of these combinations on the NHK Easy Japan website's resources page:
Hope that helps!