a double whammy
I looked up "double whammy" in a dictionary. It shows it only can be used in a negative situation.
e.g. Anne was hit by a double whammy: she lost her mother, and was herself diagnosed with cancer.
But I watched an video and someone said "If you were learn with the intention of teaching, would you focus better? When you teach something, you get to learn it twice. And that`s a double benefit, a double whammy."
It sounds like " double whammy " can be used in a positive situation. Does it make sense?

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In the UK we sometimes use double whammy in the good sense - although we use it significantly more in the bad sense.

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I’m a native US English speaker with a masters degree. Double whammy is only used for two _bad_ things happening in a pair. Your example sentence, in my opinion, is misusing the phrase.