Note that Steele and Bruce Ohr were already in cahoots for several months by then, and Steele was already established as an CI with the FBI (a cover he later blew).
Papadopoulos met Professor Mifsud in London in March, and later Misfud said he had ties to the Kremlin and he claimed Russia had dirt on Clinton. Papadopolous sent an email two weeks after the London bar meeting saying Misfud introduced him to the Russian Ambassador to England and that the Ambassador might be able to help setup a meeting between Trump and Putin.
It was what Mifsud told Papadopolous that he would later talk about with the Greek or Australian diplomat that would be reported back to the FBI.
Interestingly, there are reports that Mifsud is actually a western intelligence officer, and has no links to the Kremlin whatsoever.