I misremembered how bright magnitude 3 is. I was thinking it was towards the lower end of naked eye visibility, while it’s actually much brighter than that. There are only 171 stars of magnitude 3 and above, so the supernova would have been obvious to anyone familiar with the constellations in that area of sky, as it would have been brighter than the stars in the two nearest ones, Dorado and Mensa. But most of us didn’t miss an opportunity here, the Large Magellanic Cloud is only visible from the southern hemisphere.
The folks who got credit for the discovery were Ian Shelton and Oscar Duhalde at the Las Campanas Observatory. Shelton was taking an exposure of the LMC on a 10" secondary telescope and was having a bad night of it. He checked the plate and found a new object. In the meantime Duhalde had taken a brief break from his duties at the main telescope and took a walk outside and noticed a new star in the region of the LMC but was too busy with the rest of his night to do an immediate follow-up. Shelton compared his plate of that night with the previous night’s image and confirmed a new object and then checked outside to see if it was still visible. He and Duhalde then sent out the telex announcing it.