This is a novel claim to me. I don't think Glagolitic looks particularly like cursive Greek, and I haven't seen this idea in scholarship. What is your source for it?
Селищев А.М. Старославянский язык, 1951, страница 39 https://maxbooks.ru/images/slavimg/52.jpg
Selischev A.M. Old Slavonic Language, 1951. Page 39. https://www.academia.edu/126241874/%D0%90_%D0%9C_%D0%A1%D0%B... (PDF downloadable)
Селищев А.М. Старославянский язык, 1951, страница 39 https://maxbooks.ru/images/slavimg/52.jpg
Selischev A.M. Old Slavonic Language, 1951. Page 39. https://www.academia.edu/126241874/%D0%90_%D0%9C_%D0%A1%D0%B... (PDF downloadable)