What did they say to the ref before the game exactly? Did they say:
"We are going to have #70 report multiple times during the game in the hope that it will create confusion when we actually want to run the tackle-eligible play on the goal line because it will be #68 who actually reports"?
If not, then having #70 jog towards the ref at that point of the game clearly created confusion with the ref as he was staring straight at him as he jogged towards and then pointed at him presumably to ask if he was reporting again.
At that point, I think the Lions want to make sure the ref got it right.
My guess is that they told the official exactly what they practiced to confirm that they had the play right and was legal.
The whole point of the exercise of having #70 report multiple times and make a point to join two other lineman in the group Lions was to create confusion whether it was #70 or #68 who had to be covered when the play ran. Presumably, the Lions hoped that because it was now #68, and not #70, that would throw the Cowboys off a bit.
Any team is free to run any legal play they see fit. It's literally the official's job to understand and apply the rules and procedures, and more than the officials, the capital-R Referee specifically. This was his job, it doesn't matter if the entire city of Detroit was on the field. He had a simple task, and it was to acknowledge that 68 was eligible, and announce as much.
This is like the reverse of when they changed the rules on this, because Belichick and McDaniels found the loophole and they had all kinds of dudes reporting eligible and ineligible and coming in and out of the tackle box and whatever else during a playoff game - not one play - and THAT was confusing as shit. It sure as hell confused the Ravens, who I guess should have known better that running backs can line up in the slot and report as ineligible, and not have enough linemen and as long as the right number of players are on the line of scrimmage, even though that was something that never actually happens. And it was a big to-do and major pain in the ass to figure out as a viewer and opponent, but you know who never got confused? The officials.
Incompetent reffing and a team getting bitten by some gamemanship aren't mutally exclusive.
It still doesn't matter. You control what you can control. The Lions can't control if the referee gets confused after telling them exactly what they intended to do, that's on the league for hiring a dipshit referee who they've already failed to adequately hold accountable.