somehow, they asked for it.
"Please submit documentary evidence which establishes that you continue to be engaged in your field of extraordinary ability. Such evidence may include, but is no limited to: a currently dated letter from your present employer' copies of recent and/or ongoing publications or researches; copies of recent awards, grants or fellowships.... confirming that your continue to be engaged in your area of extraordinary ability as described in the underlying Form I-140 immigrant visa petition. "
But they responsed the RFE very fast.It only took them three days to approve the case.