To understand this passage you need to know what "carbon offsets" are. Here is an explanation from WikiHow.com:
"You can balance out your carbon footprint by buying carbon offsets. Your purchase funds [...] projects such as wind farms, which produce clean energy that displaces energy from fossil fuels. By funding these reductions in greenhouse gas emissions, you balance out, or offset, your own impact by an equivalent amount."
The writer is saying that celebrities who do things like this for the environment can appear to be hypocritical when you learn more about their behaviour in other ways. Perhaps the writer has already discussed some evidence of this.
A "hybrid" is a car that uses two types of motors, usually electric and petrol, to limit the amount of waste gas going into the atmosphere. The writer is saying that they should be driving around in "hybrid stretch limos" instead of the normal ones that use a lot of petrol. There may not be such a limo but he says this mainly to make a point.
not a teacher