There’s no way to sneak anything by the defense, in my opinion. First, I read that NFL rules do not limit the number of OLmen who can be eligible on any single play, but that it is entirely the responsibility of the lineman to report directly to the ref and to receive acknowledgement that he is eligible. #70 reported and the ref pointed acknowledgement to him. If 68 also reported, the ref would have to point and acknowledge it. Also, it has to be done in a timely fashion because there will be no pausing of the play clock for this, and no play can be run until after the ref announces the eligibility over the loud system for the defense and everyone else. Only #70 was announced prior to the play.
It was a natural reaction for a safety to see a player, 68, in the end zone and run towards him late, but 68 was never announced, so it would be unfair to the defense to allow it.
Either the ref screwed up or 68 reported late after 70 had reported and was not acknowledged or announced due to the ref already moving into position for the play. Bottom line is that without the announcement being made to the defense, of course the guy was open. Even if it was referee error, it wasn’t like the Lions were robbed of a score because the Cowboys were also robbed of being notified that 68 was eligible And being ready for it.