Is this question about limiting factors answerable?
I think your thinking is fine, but you're being a bit pedantic about it. I don't think there is any typo.
The purpose of the question is for you to understand that there are two limiting factors here: light and CO2.
You can identify points in the graph where light is limiting because there is a slope with increasing light, and you can identify points in the graph where CO2 is limiting because light no longer increases the rate, and that the plateau level changes with different CO2 levels.
Yes, you are right, there could be other yet-unrevealed-to-you limiting factors here, but there is nothing in the graph to show this. You would need to see another set of lines where increasing CO2 further does not change the plateau level, and/or where the shape changes.
Chalk it up to Occam's razor. Without further information besides what is on this graph, if I asked you to draw your prediction about what the line would look like at 0.12% CO2, you should draw another line that follows the other and then plateaus at a third, higher level.