Author here! I have no idea to be honest, I thought it was strange when I saw it in the Python version too. I'm still learning the API and it seems that

"iRacing’s telemetry comes in three variations, data written to an .ibt file 60 times a second, live data exposed to our telemetry API 60 times a second, and a session string in YAML format that contains more or less static information about the session. The YAML string is appended to the end of the .ibt file but only a small portion of that data is exposed to ATLAS."