As we are looking at antibodies in UK adults, it makes sense to compare with vaccination rates in UK adults, which is exactly what I have done in my previous post.
The ONS only publishes antibody data for UK adults, so to compare that with vaccination data for the entire population from OurWorldinData would give the wrong result.
I would imagine only a few percent of the Thai population have antibodies from infection. The majority of Thais with antibodies will have them from vaccination, as in the UK.