That quote from the datasheet doesn't make much sense when applied to the circuit provided above. The capacitor current will be very small due to the >100k (dis)charge resistor (datasheet for ref: **broken link removed**)That circuit is close, because of the >100:1 ratio of (R10 + RV1) :R9, but it is not considered to be 50% duty cycle. It also suffers from having R9 quite small. According to the datasheet:
View attachment 97272
NB:Ra in the datasheet = R9 in your schematic.