No, they don't do this. It's not even clear how they would; the closest thing would be merging based on IP or fingerprinting, but both are extremely noisy.
And the situation here is that felon_in_texas visits HN in his usual manner, views a topic he wants to comment on, creates an account on the spot, and leaves his comment. How noisy do you think the IP identification can be?
How?
Please be precise about how I can demonstrate this to myself.