Figured Out What MatPat Got Wrong!

Purple Guy is Jeremy Fitzgerald, not Phone Guy. The Save Them minigame is what gives it away. There's fresh blood scattered throughout the establishment even near the stage, and the animatronics are mostly inactive. Their inactivity gives away the fact that they're in their day modes. But this can't happen when they're open during the day.

Unless of course there's no other people expected to enter the establishment. Which would be the case on the day Jeremy Fitzgerald was on day shift. Jeremy is supposed to be in uniform for the shift, and Purple Guy is shown in uniform, badge and all.

Mangle's sprite, the animatronic sending out '10-1' emergency codes as static everytime it sees Jeremy, desperately trying to contact police, is labeled 'He was here'. Again, this is referencing Jeremy.

Then the fact that Jeremy's visage leads to '10-1' codes being sent out shows he already found himself on a criminal database. Which, I'd imagine, is exactly what murdering a child in front of a busy restaurant in broad daylight would land you. So he's Pink Guy too then, meaning they are, in fact, the same person.