NFHS made this nice and confusing in the case book. I thought they got rid of the "illegal touching is OPI" rule, then they have this:
*7.5.13 SITUATION A: Ineligible receiver A2 is behind, in or beyond his neutral
zone and has committed no act against a defender that could be considered interference
when a forward pass by A1: (a) accidentally strikes him in the back; or
(b) is muffed by him; or (c) is caught by him. RULING: In (a), there is no foul for
illegal touching. In (b) and (c), it is illegal touching and if beyond the line of scrimmage,
would also be offensive pass interference. The acts in both (b) and (c) are
intentional and not accidental as in (a). COMMENT: Game officials should be very
clear in explaining penalty options if the same act constitutes more than one foul
as listed above, as each of the fouls has a different penalty.