They both have a bit in common. They’re both communist Asian states that the US went to war with during the Cold War and did not win. But the messaging regarding the two states is a lot different. DPRK is treated like the worst dictatorship ever, that kills you and your family for even thinking that the Kims are less than gods, whilst also starving. But Vietnam, they say… nothing.
Why isn’t Vietnam demonized like DPRK?
In a vibes-based historical context, the difference is that SK still exists as a US puppet regime. Vietnam doesn’t have a frozen conflict to contend with, so the propaganda has much less usefulness. Demonizing real Korea is part of maintaining the narrative to justify the status quo forced upon the peninsula by the US.