In the official workbook, it's explained as 'the present progressive passive.'
Literal
Official workbook [in-に][topic-は] 'passive [possessive-の] present-progressive' [quotative-と] explained-[passive-されています].
Another metalinguistic sentence from the English grammar education domain. 受け身 'passive voice' (literally 'receiving body') and 現在進行形 'present progressive form' are standard Japanese grammar terminology. The passive されています distances the speaker from the claim — 'the book says, not me.'