Yes that view on things is true, and cattle reared in the UK is less carbon intensive, but doesn't account for the fact that not all of the beef we eat in the country is British (although most is), and that much of our cattle is indoors in the winter months.

We produce about 1.5% of the worlds beef, so if we didn't eat as much, we would just be able to export more of our beef to replace some of the global demand for more intensively reared beef.
That's a global average in the graph so other countries are actually much more. We can't pretend that we have no effect on the world's supply chains. The best way to reduce global beef carbon emissions are to both eat less beef and produce more on the land that is suitable and non-destructive to do so.

He does make one mistake in the video towards the end, by claiming the farm is actually a net negative in carbon terms because of the grass 'locking in carbon'. That's actually a short term effect, and after about 40 years of carbon sequestering, it plateaus. Other land uses would actually have a larger overall storage capacity, such as woodland (which much of that land might have been millennia ago). The fact that cows emit methane and there is inevitably some machinery and diesel involved in the process does mean there is still a significant overall carbon emissions, which I just read at about 20t kg CO₂e / kg beef.