SAGE Methods subsequently said that the earlier tweet was factually inaccurate and sent without sufficient context. They offered an apology for tweeting inaccurate information and posted a link to the UK’s ONS site for correct information. They also deleted their original tweet.
ALT Tweet by SAGE_Methods indicating, "Our earlier tweet was factually inaccurate, for which we apologize. It was sent without sufficient context checking. ONS guidance for Census 2021 questions on sex and gender identity can be found here: https://www.ons.gov.uk/census/censustransformationprogramme/questiondevelopment/genderidentity/census2021finalguidanceforthequestionwhatisyoursex"