Yes, I know it's not technically just methane, but methane is its primary constituent.
"Fossil gas" is also probably a suitable term, but I like "fossil methane" because it gets that spooky chemical name benefit.
The name Natural Gas arose long before there was any effort to greenwash anything. It was in comparison to Coal Gas, which was artificially produced from coal and in use before Natural Gas came to market. Acting like this is some kind of greenwashing propaganda conspiracy just makes you look ignorant, and as a result it makes the whole movement look bad.