Interesting. I think what would be so hard about doing such an estimation is that most of the damage is just so far removed from us end consumers. It seems to me, very hard to extrapolate what one gallon of gas burned or one hamburger of meat eaten actually equates to on the production end of the spectrum. Care to share any more details?
Using https://www.eia.gov/tools/faqs/faq.cfm?id=307&t=11 we get us co2 per gallon, and https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles#Fu... gives average miles per gallon, which with units (gnu tool) translated it to about 8.6 miles for 3kg co2. 8.6 miles is, depending on driving speed, a reasonable estimated of 10m driving. So if a person commute time to work is 5m, and 5m back, the co2 should be similar to a person who eat meat-rich diet but who work from home.
Giving the meat vs vegetarian study authors the benefit of the doubt with respect to their calculations of greenhouse gas emissions from "production, transport, storage, cooking and wastage of food", and considering that on the commuting side of the equation you're only considering the emissions from burning gasoline (ignoring drilling/extraction, refining, and all the transportation that happens in the middle), the disparity must be even worse than you suggest. Perhaps a little ironically, the headline of the Guardian article says exactly the opposite.
The article title is a bit ironical, but then the article title is just derived from the quote and don't provide any arguments.
I can only speculate, but I suspect there are a few reason how one could interpret data that I have seen elsewhere. One is that while CO2 from cows are higher than from cars, those numbers don't take into consideration that people can choose to stop driving but not stop eating. If you replace cows with vegetarian option, that is still 2.9kg CO2 being released per day per person. A stop to driving is 0kg CO2.
The second aspect is that there is likely more people who don't drive cars than people who don't eat meat. If we are talking about what individual people can do, stop driving is still the best way to reduce ones environmental impact, and I suspect that the average amount of car owners on HN is a bit higher than the global average. Once that box is ticked off, discussion of meat vs non-meat options is a bit more relevant.
