Is the equinox absolutely true east everywhere?
The celestial equator's plane intersects the horizon due east and due west, no matter where you are on Earth (except at the poles where the horizon is the celestial equator).

Those that have the sunrise at the exact time of the equinox will see the sun rise in the east (90º). For the rest, it will be too late, the sun will have made the crossing, and it could be something like 90.00001º or 89.99999º, although it will still be perceived as due east.

The last equinox was March 20th, 03:50 (UTC). At that moment the sun was rising very close to Maputo, Mozambique (table), so everybody on that meridian saw the sun rise in the east, exactly at 90º.