After 4.Ng6 N8c6 5.Rh3 the threat of 6.Nh8! does not give Black an easy way out (to find over the board). It seems Black is forced to give the piece back (5... Nxd4 and 6... Ne2/f3+), and with equal material White can still play on – no trivial draw for Black.
So, my claim is merely that the comment
"4.Ng6. This does not contain any real threat since 5.Nxf8 gives Black two pieces for his rook and 5.Qh8+ is calmly met by ...Kf7."
completely misses the idea of 4.Ng6 (why would we sac a piece in order to "win" an exchange on f8?) and is too dismissive of this move compared to the relatively kind comment
"4.Rg3. White thought this was winning but it only turns out to lead to a perpetual check. However, if a draw is what you were after then this move fits the bill nicely."
So, my claim is merely that the comment
"4.Ng6. This does not contain any real threat since 5.Nxf8 gives Black two pieces for his rook and 5.Qh8+ is calmly met by ...Kf7."
completely misses the idea of 4.Ng6 (why would we sac a piece in order to "win" an exchange on f8?) and is too dismissive of this move compared to the relatively kind comment
"4.Rg3. White thought this was winning but it only turns out to lead to a perpetual check. However, if a draw is what you were after then this move fits the bill nicely."
4. Ng6 is said not to threaten anything because Nxf8 is nothing and if Qh7+ then simply Kf7. That's true, but the comment is incomplete. The point of 4. Ng6 is neither of those options, instead there is a real threat to play 5. Re3-h3, 6. Ng6-h8! (that's the point) and if Black gave those two moves for free then there would be no defence against 7. Qh7# since if the f8 rook leaves, then 7. Qf7#.
Thus, 4. Ng4 is the clearly winning move, but after 4. Ng6 Black doesn't have a trivial draw, does he?