Reproducing the surface behavior of a program, no matter how faithfully, is not in itself copyright violation if it's a cleanroom implementation. But int this case it's not to write the new one, the developers studied (and manually translated to C++) the original code, not just the program's behavior. So this is more of a case of a derived work, like a translation of a novel.
And Sony vs Bleem (or the IBM BIOS reimplementation) already set a precedent so that doesn't really matter anymore. Look at Wine. Or Exegutor. Or DOSBox.
All of them totally legal reimplementing either prior look and feel and functionality.
> The code of computer programs are excluded from design protection, but visual aspects of software are very commonly protectable as long as they are ‘new’ (i.e. not a direct copy of anything that has come before) and possess ‘individual character’ (i.e. that the design produces a different ‘overall impression’ than anything that has come before)
I'm no expect, but Chris Sawyer style games certainly provided a unique overall impression to me. Whether it needs to be a registered design or not I couldn't say, but it's not going to be cheap to find out.
More recent battles have relied on Trademark and Patent law rather than Copyright, but "Look and Feel" is still a legal grey area
Wine literally copies both the Win32 UI -needed to respect that for interop- , some of the kernel functions and Win32 which is just an API implementation and not copyrighteable per se. If not, we woudn't have GNU. Or Microsoft services for Unix.