Fireballs can be colorful. Small streaks are too dim to trigger your color receptors, but bigger streaks (fireballs) are bright enough to look colorful.

As the article said, it could be magnesium. It could also be energized oxygen atoms, because at the height of the fireball, the atmosphere will be quite thin.

The streak is just due to alignment and optical illusion. It burned up very high up and you'd get mostly falling dust.