FMCW Waveform Irregularity with Default Code

In the below graph, why does the frequency increase, then decrease across the FMCW chirp/sweep time in the Amplitude v Time domain graph but not in the Frequency vs Time domain graph? This is the default FMCW waveform for 'SweepDirection' = 'Up', which you provide on your website here (https://www.mathworks.com/help/phased/ug/automotive-adaptive-cruise-control-using-fmcw-technology.html?searchHighlight=acc%20fmcwwaveform&s_tid=srchtitle).

Additionally, when I try to change the 'SweepDirection' to triangle with the provided code, it does not switch either graph.

Thanks.