How do universities decide whose English needs to be tested for admission?

When Muhammad* applied for admission to a postgraduate degree at an Australian university, he was asked to show evidence of his English language proficiency. Acceptable evidence included achieving a specific score on a commercial language test such as IELTS or TOEFL. Muhammad was upset to discover that none of the following counted as acceptable evidence of his English language proficiency: that all his prior education had been through the medium of English, that he was employed as university lecturer in the English department of a university in Bangladesh, and that he had published fictional and non-fictional writing in English.