Translation:I actually still have not read your text message.
I think NasuSamaruk0's point was that because this course uses simplified Chinese characters it must be teaching mainland Chinese usage, since simplified characters are used on the mainland. And on the mainland "短信", not "简讯", is used for "text message", whereas Taiwan uses "简讯" ("簡訊").
However, the course also accepts traditional characters, and I doubt the aim is to completely exclude Taiwan usage. In my view such usage should be reported as acceptable if it's rejected, though I think it's reasonable to have mainland usage as the default.