"Cha robh e a' sreap?"
Translation:He was not climbing?
Standard Gaelic grammar, as far as I know, doesn’t allow you to form questions this way, you would need to say: nach robh e a’ sreap? with negative question particle nach (does not?, is not?, …) at the beginning. That would translate to English was he not climbing?, wasn’t he climbing?.
cha robh e a’ sreap? is just really Scottish equivalent to English he was not climbing? and would be considered ungrammatical when confronted with traditional grammar.
I guess this is very colloquial and the course authors want you to learn colloquial ways people speak, otherwise I’d report this whole sentence as an error.