That is not it; when you don't call the function to warmup the baseline values are not set and hence the sensor readings are useless. 

The driver is poorly written…

After reading the code, there is a baseline reading in the ‘Warmup’ routine. When you don't call warmup the system is not initializing the baseline reading and all values are wrong. This driver is poorly written and worse of it is that the values being read are all over the place.

Exposing the sensor to methanol only also triggers nh3 ch4 and other compound readings. 

can't recommend this sensor to anyone except for a rudimentary detection of something in the air.