As for Illegal Touching, that is completely independent of the A player stepping out of bounds voluntarily. If Team A was (as a whole) was not yet eligible to touch the ball, then yes, you may have Illegal Touching. But, if the ball had reached B's restraining line or had been touched by B, then no - not illegal touching.
As for the A player stepping OB voluntarily, he is prohibited from returning to the field of play. However, if he does return (requires that he actually touch the ground inbounds), he has only fouled for returning to the field of play. Any action by him is governed by all other applicable rules. If he blocks, tackles, touches the ball, etc. - those actions are governed on their own merits. The fact that he does them are not fouls in, and of, themselves.
In this case he had stepped OB voluntarily, but was airborne when he touched the ball. An airborne player is neither inbounds nor out of bounds. So, his touching of the ball does not make the ball dead (he isn't OB). It might be Illegal Touching (as noted above), but it might be legal. It might be illegal batting (don't know if it was forward or backward), but it might be legal.
But the touching of the ball and the fact that he had stepped OB voluntarily are unrelated issues.