Heaney, as you have suggested in your third paragraph, was a terrific translator, his finest translation being Beowulf of course.
The role of a translator is critical; translators must know more than the linguistic differences between the languages; they must be able to understand and convey the cultural similarities and differences between the source and the target languages. To do such translation requires more than technical language skills; it requires the ‘right’ awareness of the role of translation and translation issues as well.
In terms of the above passage, I think Heaney hits the right note when he tranlsatestranslates it, the conveyance of the poem using a slight re-wording may annoy especially if the original author had not intedendedintended it this way but that is never Heany's focus. It is to tell the story from a new perspective.
To borrow his own words, Seamus Heaney, the man and his poetry, forever catches, 'the heart off guard, and blows it open'.