OP your DH is wrong.
Your DH isn’t even half Welsh, he’s 100% English nationality.
However, he is of Welsh ethnic origin. Some people would call this Welsh-English, nobody should call him Welsh as he was not born in Wales, unless they are referring to his heritage and not his nationality.
For example, someone born in Birmingham is not a Yorkshireman even if his parents were both born in Yorkshire.
I have a friend of English race that was born in Germany, has British nationality and is of Indian ethnic origin. No wonder most people interchange definitions wrongly.
https://www.devon.gov.uk/equality/guidance/diversity/guide/race#:~:text=%27Race%27%20is%20a%20social%20construct,language%2C%20or%20distinctive%20shared%20culture.
“Race’ is a social construct and not a biological fact as explained in this BBC Video. Race covers: nationality (for example, British), national origin (for example, English), skin colour and ethnicity or ‘ethnic origin’. Ethnic origin is defined by a shared history/ancestry, language, or distinctive shared culture. Nationality is determined by what is on your passport (British) and national origin is the country where you were born (English).”
https://dbpedia.org/page/Welsh_people
“The Welsh (Welsh: Cymry) are an ethnic group native to Wales. "Welsh people" applies to those who were born in Wales (Welsh: Cymru) and to those who have Welsh ancestry, perceiving themselves or being perceived as sharing a cultural heritage and shared ancestral origins. “
http://projectbritain.com/nationality.htm#:~:text=People%20born%20in%20Wales%20are,are%20Welsh%20rather%20than%20British.&text=Are%20the%20people%20in%20Britain%20ethnically%20diverse%3F
“People born in Wales are called Welsh or British and can say that they live in Wales, Britain and/or the UK. Most people in Wales will say they are Welsh rather than British.”
Similarly people born in England are called English or British.
So he is English (nationality) and Welsh (ethnicity).
But people often want ot be what they are not and in this crazy world we live in people can apparently identify as anything can’t they, even the wrong sex or species, so just humour him.