In answer to your points raised we have summarised the Somali population estimates below and provided notes accordingly
England & Wales figures
QS203EW gives country of birth= SOMALIA 101,370
QS209EW gives ETHNIC GROUP 45,475(Somalai) plus 6,249 (Somaliland)
CT0010 gives ETHNIC GROUP 45,475(Somalai) plus 6,249 (Somaliland)
The 101K from QS203 are only those people born in Somalia, not their descendants who may consider themselves Somali despite being born elsewhere.
The 45K (and additional 6K) from QS209 are only those who specifically wrote in "Somali" under Black Other - We know that the majority of people from Somalia (and elsewhere in Africa) will have ticked the Black African box, rather than provide a text response.