It seems like both you and Thiel botched this one. Meat consumption is a gigantic environmental problem, but methane isn’t the chief culprit as to why. The issues are that the average American has a carbon footprint about 1.67 times that of the average American vegan, cows consume a lot of water, and industrialized meat production has long led to deforestation all over the globe.
This isn’t even getting into the animal cruelty aspect of industrialized meat production.
Bottom line: there’s nothing wrong with not eating meat, even if a hack like Peter Thiel has his own agenda for wanting you to not eat meat.