Which is very important, because no airline is going to validate a passenger's individual circumstance to determine whether they qualify for a visa waiver program for a specific country. If someone presents a passport that normally qualifies for a visa waiver program, the airline isn't going to make them show a visa, even if their individual circumstance requires it. So OP really needs to figure out how Japan actually recorded this and what implications this has for their international travel going forward.

If this, or something similar is what was presented then I could easily see an airline employee mistaking it as being a visa, especially for destination that prior to the pandemic did not routinely require visas. Regardless, whatever the tour guide and passenger received they thought it was the visa, so there's no reason to expect an airline employee is going to think anything different. Visas come in all shapes and sizes, airlines aren't in the business of validating it as being authentic or even the correct visa for a passenger's circumstance. All they need to do is show due dilligence that they reviewed the entry requirements for the passenger and they presented what appeared to be the correct documents. The validity of the documents to the individual's travel situation are up to the individual countries border staff to figure out, else we might as well deputize the airline gate staff for every country they manage a departure too if we're going to expect them to make advanced determinations on visa validity.

This, of course assumes this was actually a purchased J fare and not upgraded with some form of upgrade currency.