No matter how cautious he is, the name "Silver Scalpel" and "Trying to reawaken the dead" will inevitably come up in different places. He's used a lot of different names, yes, but he has used his own a few times (You said that yourself, I think), even if only in passing. Undoubtedly the Cult of Laughter will probably have had spies and such out looking for him as well... They could have spread such rumours as well... Anywho, I don't think Amaretto has said anything that would tell of knowledge he couldn't possibly possess, at least not yet.