I own the complete works of Emily Dickinson--it's tedious, but one can look through the entire thing. There's only one use of the word "swallows" and it's not about birds.

So... maybe they misattributed the poem. Except that I don't find any reference online to the lines in Spanish, either, except in their posts. Or *maybe* they did the translation themselves... except that, see above, no swallow-birds in Emily Dickinson.

Truly a mystery. It's very Emily Dickinson-esque, reminding me of hallucinated fake quotes I've seen but who knows?