My impression of Vietnam is that people there are pretty chill indeed, but also that answering truthfully in such surveys might not be in your best interest if you are a local.
They're authoritarian, but not that kind of authoritarians. I feel like they have an easier time criticizing their government than Cubans,but they do it less (Cubans will imply worry/dissatisfaction rather than say it, Vietnamese will say it plainly). It's a bit like China pre-Covid (I never went post-covid, maybe it hasn't changed), Vietnamese overall like/trust their government so they'll avoid talking shit about it, but without the weird nationalist 'pride'/defensiveness/victimhood that I found in China.
[edit] I compared it to Cuba/China because all three of them are communist countries, and I visited them all, but probably comparing Vietnam to its southern neighbors could be more appropriate
