Bitcoin is not traced because its users can make it without giving their real name, so I do not think you can catch them how they know you have btc while BTC does not mention the name of the BTC owner.
I think its hard to trace if you buying a bitcoin or you hold a bitcoin because i think if you have a bitcoin your name will not listed so the government did not trace or did not know you even the creation of bitcoin its hard to know how much more the investors its hard to trace.