Are you unaware of how dictionaries are created and kept up to date?
Let's say you are - apart from being documented as the primary use in the UK by the dictionary what type of evidence would you accept?
Ofcom?
https://www.ofcom.org.uk/__data/assets/pdf_file/0022/91624/OfcomOffensiveLanguage.pdf
"... Racist language such as ‘coon’, ******** and ‘
wog’ were among the most unacceptable words overall; they were seen as derogatory, discriminatory and insulting. Many participants were concerned about these words being used at any time, with their use requiring significant contextual justification. Other words in this category were more open to debate; participants had differing views about their acceptability after the watershed, based on how insulting they were perceived to be. ..."
Given the use of "UK" in their posts about this it might indicate they were talking about the UK?