Did you sand or dress up the flywheel? It's strange to have heat cracks with no evidence of overheating. As to the public being in harm's way from a flywheel failure, that would be your last concern if that comes through the floor pan.

Oh, BTW, I would not run that flywheel if the rest of it has that pattern. Multiple radial cracks in such close proximity aren't good. I'd wager that if you checked that with dye penetrant it would look like an alkali flat.