Did you look into that claim at all? Michael Twaddle's "The Ending of Slavery in Buganda" seems to be one of the central writings about the end of the slave trade there. It seems that the connection to the Indian Ocean slave trade was through trading with Zanzibar. British colonial administrator Frederick Lugard ended the slave trade with Zanzibar, and freed the slaves there. I've looked at other sources as well, but from everything I can find that seem to be the extent that Buganda "helped end" Indian Ocean Slavery (there British colonial administrator helped end it).

If you read historical research on the ending of slavery in Buganda, it's similar to what I said. It was pushed by the British, often against intense local opposition.