>Chernobyl is the only accident in commercial nuclear history that has exposed people to large enough doses of radiation to poison and kill them.

This is not true, it wasn't the only and not even the first. Some examples are collected in this list: https://en.wikipedia.org/wiki/List_of_orphan_source_incident...

The argument is also an annoyingly common attempt to sell the idea that nuclear power is not dangerous because there haven't been worst-case accidents yet.

But we know they can happen and what the consequences would be, so it's entirely irrelevant what has happened so far.

Both Fukushima and Chernobyl are active incidents ongoing as we speak, we don't know how bad even they will turn out to be.

This Wikipedia article seems completely irrelevant to the quote you posted. They're clearly talking about commercial nuclear energy plants, not orphan sources from radiography and radiotherapy machines.