Does the sentence 'Boy, are my arms tired' mean 'Boy, my arms are tired.'?

I found a meme that says 'I flew in from (wherever) and boy are my arms tired!'. I can understand what's funny about this meme but I can't understand why 'are my arms tired!' is used instead of 'my arms are tired!'. that's not an interrogative sentence, right? why does there have to be an inversion?

After a short interjection of amazement / delight / relief / exhaustion, inversion is not uncommon but only with a limited subset of interjections:

• "Wow, is she having fun!" [YouTube; Grandma sledding]

• "Gosh, was he a looker!" [Facebook, via Google

• "They beg but man are they cute!" [Tripadvisor.com / Santo_Domingo]

• "Boy, am I glad to see you!" [Farlex Dictionary of Idioms 2015]

This is discussed in an article by [Andersen and Aijmer in The Pragmatics of Society]:

Subject-Auxiliary Inversion (SAI) is one standard index of the exclamative clause type.... This inversion of standard word order instantiates one type of exclamative sentence and is itself a marker of emotional involvement ....

Occasionally, the inversion-form exclamatory appears without an overt interjection:

• "Am I glad to see you!"
• "Is he one lucky guy!"

It does appear at first glance to be an interrogative due to the subject-auxiliary inversion. However, in this instance, the closed interrogative (yes/no question) indirectly conveys an exclamatory statement, the implicit meaning being close to that of the positive exclamative:

How tired my arms are!

The understood meaning is that the speaker's arms are very tired.