In this context, "in a row" means in sequence, or consecutively. So the writer guesses three or four times, without being interrupted. "Low" is a very different word, of course.

'In a row' means one after the other, continuously. The system described in the sentence looks like: I guess I guess I guess You guess You guess You guess You guess I guess I guess ... We don't just get one guess at a time, but rather a few before we swap over.