Accuracy of bike rental sample

[andyste1]

Not sure if this is the right place to ask. I'm new to ML, and looking at the chart at the bottom of this page, the predicted results look pretty poor to my untrained eye, especially the last few points. Why is this? Would more training values help? I appreciate forecasting is merely that.

Can I also ask, the data in this sample consists of just two columns: "year" and "total rentals". Am I right in saying this algorithm can deal with many columns, and isn't restricted to two?