Hi Max,
What you described looks correct to me. ADXL362 used overmolded laminate package, the bottom and side edges of the laminate could be exposed to light. Although there are metal traces embedded in laminate, the light can still possibly go through, light with certain wave length may be able to hit the transistors. Light is a powerful leakage maker according to photo-electrical effort.
As ADXL362 is a micropower part, its circuit impedance is much higher than other products. That makes it more sensitive to induced leakage.
As you said, in production, all the parts will be encased, then there is no such issue.
Hope these can help.
BR
Neil