>>9268429They're reusing the Bizarro body which has sculpted traditional Superman boots (with a V shape). Rebirth suit had inverted V shaped boots with a red trim, so they just painted the inverted V. Honestly they should have just painted the sculpted trim red, most wouldn't even notice the V being inaccurate.
Personally I prefer this, as I'm planning on painting the whole boot red for a Rebirth 2.0 look (which went back to the classic boot shape).