Here's the context I'm asking about:
"My dad was funny. That was one of the reasons all of my childhood and college friends loved him (and man did they love him)”.
I understand that "did they love him" here is an exclamation rather than a question. It means "wow, they really loved him”, or does it mean something else?
Also, is there a name for this grammatical rule? I couldn't find anything on google and I want to learn more about it.
This is a fairly flexible turn of phrase that can be used to turn a statement into an exclamation of surprise. Any interjection and any auxiliary verb can be used; the sentence is simply stated in question form with the interjection immediately before it, usually with no punctuation between them. Stress can fall on the interjection, the subject, or any other important part of the sentence.
Some examples:
"Boy does that stink!" ("Boy" = somewhat outdated, but strongly associated with this structure)
"Man would I love to be with her again."
"Wow is that spicy!" ("Wow" = less idiomatic, therefore creating particularly strong emphasis)
"Sure his music is good, but holy sh*t can he drive a crowd too!"
While flexible, this structure is, all told, not that common; I advise not to overuse it.
This is called a rhetorical question. There are many uses of questions that don't expect answers.
Rhetorical questions are used to engage the reader/listener. This particular pattern also uses another rhetorical technique, the exclamation "Man!" As well as engaging the reader, it also intensifies the phrase. You expect your reader to think "Ah yes, they loved him a lot!", and since the reader has actively worked out the answer to the question, they are more likely to remember it than if they were just told it.
