Quick answer
Announcing a gift you never gave is weather that promises and does not deliver. The verse picks the cruelest possible image for it.
Read both lines
In a farming economy clouds and wind were the visible signs that the rain was coming, and everything depended on it. So the comparison is not that the boaster is merely hollow. It is that he raises hope in people who need the thing, and then the sky clears. The disappointment is proportional to how badly the rain was wanted.
The Hebrew makes the gift a מַתַּת־שָׁקֶר, a gift of falsehood, so the lie is attached to the giving rather than to the giver's character in general. Jude uses a close cousin of this image for people who promise and give nothing, calling them "clouds without water, carried about by the winds" (12), which is a different context making the same observation about the same kind of person.
Related: Jude 12 · Proverbs 20:6 · Proverbs 19:22 · Proverbs 27:1
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.