I think you have all the right to ask that participant to return their submission. I’m not sure if the best/correct way is to reject it tho. I read from the page you’ve shared:
Please note that rejections can only be made on the basis of inconsistent screening responses if the questions within your survey are presented exactly as they appear on Prolific . This is to avoid rejecting participants because of subjective misinterpretations, arising out of any differences in wording between your screening questions.
So, by interpreting that “exactly”, the question used in the survey should be identical to the default pre-screener available in Prolific. Could you clarify what you mean by “were approved via email”? Were you in touch with Prolific Team, and they approved your question?
If one wants to be strict, I’m not sure whether your case lies in the list of admissible cases for rejection, which is available at the following page:
If I were you, I would probably send a message to the participant and ask them to RETURN their submission. You could possibly grant them some bonus payment (lower than the full payment you give to other participants) as a form of gratitude.