There was a related topic a while back in this thread: Volcanos, Humans and Global Warming. In summary, while volcanos in general release a significant amount of greenhouse gas, a far greater amount is released due to human activity.
I’ve heard it both ways too. Probably both are either unsubstantiated, or vary depending on what you consider a greenhouse gas.
Of course, the term “greenhouse” is a misnomer. A greenhouse stays warm not because it’s trapping radiation. It’s because it doesn’t allow air to move from a central area; that is, its interior.
The only thing producing a greenhouse effect on Earth is gravity, which doesn’t allow most warmed gases to escape from the surface of the planet.
I was all ready to post how wrong you were and about how greenhouses do trap radiation, but I looked it up and you are right. Hot damn, you learn something new every day!