A decade ago, when I was Talking About Cryptocurrency (approving), in presentations etc., this was indeed a very frequent assumption of my audience. They would be confused and/or shocked when I referred to earlier in the presentation to show that no, every transaction on the blockchain is visible to everyone, forever, otherwise it can't even work.
I suspect a lot of the shocked response was due to the (unspoken) follow up question “then what the heck is the point of this, why would I use this?”
But I can see why the assumption comes along. Cryptography is all about secret, obscured communication; why wouldn't cryptocurrency be about secret money transactions?
At least now we can Talk About Cryptocurrency (derogatory) and dispel that assumption, where we can.