BS. He is supposed to refer if he sees a crime. There is no in between. That is NOT the standard by which he operates.
"We are sure there is a crime there. We just could not find it so we had to not say it..." Complete and total BS.
This is a somewhat special case. He certainly could have referred with a recommendation, even knowing that there could be no actual indictment. That, however is not where the line was drawn.
Mueller decided he didn’t have a case to even attempt or recommend an indictment.