Unfortunately, Heritage Auctions isn't infallible when it comes to authenticating props. There's a thread here about a supposed hero phaser from TOS that fetched big bucks, but its provenance is very shaky and the details of the prop itself have convinced people far more knowledgeable than me that it's a fake.
That doesn't mean anything about your purchase specifically, could very well be genuine, but HA and other auction houses aren't perfect.