I don't think we have an alliance with Vietnam. AFAIK, there is no US base or military agreement or anything indicating a higher relationship than trade partner.
In fact, a few times DC sent some diplomats to Vietnam, the govt over there responded by sending their diplomats to China. Basically saying they prefer China over the US. It makes sense to them since China is closer and have higher trade value than the US. But because of that I don't see how Vietnam can be a "strong ally" to the US.
I read this a few years ago, not sure how much it reflects reality. Anecdotally, immigration from Vietnam is still strong, except the more recent immigrants I've met are pro-communist (as opposed to the first and second generations of Vietnamese immediately following the war).
I'd imagine that the US and Vietnam are allies in the same way that Israel and Egypt are allies. Publicly, they have to show opposition, but privately they work together economically, militarily, and everyone knows that they aren't actually at odds with each other.
It is just an old poll. I don't think it is relevant. Public opinion doesn't mean much in authoritarian countries. It is what the Vietnamese government is doing that would reflect what they really think.
It is more likely that Vietnam is playing both sides and try to appease both China and the US. But no way they are an ally or even a potential one.
