Ah, I see the source of your confusion now. The actual situation as given to us is not that there are 4 visible cars on a table. It is that there are 4 visible

Ah, I see the source of your confusion now. The actual situation as given to us is not that there are 4 visible cars on a table. It is that there are 4 visible cars on a table that contain a number on one side and a color on the other side. We are being told to verify the statement: "Of the 4 cards placed on the table, which have a number on one side and a color on the other side, if the number is even then the other side must be blue." If the color/number statement was left out of the original problem/video (it isn't) then your argument would be true, as it would be an assumption that is not listed and we would need to flip the 5 as well. E: And I suppose the blue card since it could have green on the other side.