Following up on this, I eyeballed the images in this one: https://iopscience.iop.org/article/10.1088/1538-3873/ae0afe

The brightest stars in all of the images have a clear 4-pointed pattern. The brightest transients _do not_ show this pattern.

This is obviously not definitive, and the fainter stars are harder to eyeball the PSF, but it does provide some evidence to support the hypothesis that the brighter transients could be due to gamma ray exposure of the film rather than flashes in the atmosphere or space.