What is the meaning of load of a line?
From the documentation:

The line flow pie charts are used to indicate the percentage MVA, MW, or Mvar loading of a transmission line or a transformer. The degree to which the pie chart is filled shows how close the device is to its limit (provided the device has a nonzero limit). A line flow pie chart becomes completely filled when the device's flow meets or exceeds 100% of its rating.

So rather than current, it is indicating power (Real, reactive, or true).
https://www.powerworld.com/WebHelp/Content/MainDocumentation_HTML/Line_Flow_Pie_Charts_on_Onelines.htm