This is interesting because my boyfriend caught me saying “I bought this t-shirt offline the other day”. And since I am studying Semantics at the moment it made me really think what the word I was saying meant.
I see it as two separate words “I bought this t-shirt off line the other day” so like the sentence “I bought this off eBay the other day” means from, i.e., “I bought this from eBay the other day”. Or “I bought this off TV” (people say this – and it’s a similar problem). Thus in this context the off line really means “off online” or “off the internet”. Where offline is the opposite of being online, I think off-line or off line indicates that you bought something that was on the Internet — but now that you bought it, that very t-shirt is no longer on the Internet so it seems to make sense to say you bought it off-line which means “off the line”, “off the Internet”.
Rather than online being a state, it is more of a noun phrase “line/the internet” and like “I bought this off the television” the the is dropped for ease of speech.
So I think it works and it’s neat. There are plenty of words in the English language that have different semantic meaning in different contexts. eg. “I am meant to be finding treasure at the moment” vs “I’m finding this difficult right now” (not a great example, but I hope you get my drift).
It’s interesting how technological advances affect and modify our speech.