Translation:The wind blows strongly.
That's not what the sentence says. Read the rest of the comments in the thread. 強い風が吹きます would mean "(a) strong wind blows"; this sentence says 風が強く吹きます, "(the) wind blows strongly". Changing つよい to つよく and changing the position turns it from an adjective into an adverb, turning "strong" into "strongly".
Although you're right from a literal standpoint, I don't think that was Rael763700's point. He said that the correct answer sounds unnatural, and he's right. There's plenty of other times in Duolingo when nonliteral but more natural sounding answers are accepted.
There's more real world merit in giving a natural translation especially when it doesn't change the meaning, so I would agree with him that "A strong wind blows" should also be accepted as a correct answer
If we are to resurrect 1+ year old comments, then here are my two cents: I would argue that in the use case of Duolingo - learning a new language - it is essential to differentiate between things like adjective/adverb, because if you do not and instead accept more natural translations, then you could end up confusing the user.
Also, I think that this sentence was ill-chosen and another sentence with more natural English translation should have been chosen for presenting learners with Japanese adverbs. Hopefully the reworked Japanese tree will prove better in this regard.