They really should learn how to run their vertical axis down to zero . I see no need to risk the accusation of using graphs with a lie factor. it'll still look a dramatic increase starting a zero. They can even add a horizontal line at lowest recorded level if they want to emphasize that difference. They're also open to a bit of criticism on the time-axis about the difference between lowest 'directly recorded', and other longer term estimates of the range of atmospheric carbon dioxide.
I think it is better to acknowledge those estimates and refer to the available evidence on how different the world was and what types of life and ecosystems seem to have been most common. Otherwise they can get "Well akshually it might be 'uncharted' but it's probably not 'unprecedented' " . . . . https://paleo-co2.org/co2pip
Based on these estimates it seems plausible that early primates experienced atmospheric carbon dioxide levels higher than today. The important part is that they'd not have lived very similar lives to modern humans, maybe like small lemurs or something.