What does GLOW mean by DPO?

Jennifer • FurMama🐶, AngelMama👶🏽, & a RainbowMama!🌈
I know DPO means Days Past Ovulation but here's what I'm wondering:
This is my first month tracking bbt. I noticed on my chart there is an area of green that starts tracking DPO. Is that there because GLOW is tracking from the date they already predicted as my ovulation day, or is it updated there because GLOW thinks I ovulated according to my bbt tracking??