I'm asking not about what they were asked to bring, but what the staff actually checked.
There is a comedian/talk show host, Bill Maher, who has a regular segment he calls "I don't know it for a fact, I just know it's true." It is intended to be a comic routine.
In that vein, being a bit tongue-in-cheek: "I don't know for a fact, that if an applicant does not have his passport, that is when they will ask for it during the oath check-in, I just know it's true."
Actually, I do not know that is true. I doubt not having one's passport is something which would trigger IRCC to require it at the oath check-in. (That, otherwise, would be superstition.)
But whether the ratio of those not asked to show their passport, versus those asked, is five-to-one, ten-to-one, even fifty-to-one, if the one applicant asked is without his passport that could be a real problem . . . perhaps having other obviously authentic forms of identification and a good explanation for not having the passport will suffice to avoid any significant repercussions, but otherwise it is easy to see this scenario turning things sour in short order. Perhaps the only consequence would be a delay, short or long, but it could result in a step back and involve further non-routine processing. It would be rather sad to get that far and end up having to jump through more hoops and wait a lot longer.
Remember, the chances of falling are only one part of the risk-calculation. How far or hard the fall would be is another very big part of the risk-calculation. The odds are very good when playing Russian-roulette, five to one NO problem. Given the potential loss, however, those odds are NOT good enough to play, even if playing for a hundred grand or more (not by my calculator anyway).
In any event, forum accounts of the oath experience tend to be perfunctory if not superficial, few offering any more than minimal details about the formalities. I have not personally kept track of the extent to which applicants are reporting further document-checks, or the lack of any further documents check, at the oath event. Most do NOT report one way or the other. By this stage in the process, most are focused on celebratory elements in the experience. Note, for example, even when CIC was going through a ridiculous phase in which there were monitors at the oath ceremonies watching to be sure every candidate stated the oath out loud, and denying citizenship to applicants who failed to clearly state the oath out loud, almost no one was reporting this much in the forums. Almost everyone knows the formalities and complies with them. They have the required documents. They state the oath. They sail through the oath ceremony. They celebrate becoming a Canadian citizen.
In other words, it is obvious few (at most) gamble at the taking-the-oath step. It is possible there are minimal accounts of problems arising from failing to present a passport because few are asked to present a passport. It is just as possible, and very likely, that there are minimal accounts about not presenting a passport at the oath ceremony because almost everyone follows the instructions, brings their passport, and there is NO problem . . . and few if anyone taking note whether anyone else was actually required to present their passport.
BOTTOM-LINE: Anecdotal reports will rarely, if ever, provide assurance that it will go OK if the applicant does not follow the instructions. They can indicate the odds are very good. They can never guarantee there will be NO problem.
Gamblers place a bet at their own peril.