A residential lot existing at the time of this chapter's adoption, which does not meet the lot area/dwelling unit, frontage, front, side or rear yard setbacks listed under the conventional development option shall not be considered to be nonconforming in lot area/dwelling unit, frontage, front, side, or rear yard setbacks if it meets the minimum lot area/dwelling unit, frontage, front, side, and rear setbacks of the cluster lot development option.