Yes I think they mean it's a continuous line, not a "straight" line. As in the line is uninterrupted (continuous). It's also possible they mean the line qualifies as a nonlinear function since it also doesn't double back over itself (A function is a relationship where each input value (X) will create only one output value (Y)).

Math is hard. Describing lines like this is math - calculus actually due to the curve, and actually not just basic calculus but vector calculus because it involves an x,y, and z axis. Most laypeople will struggle to describe a line with the correct jargon.