So you seemingly missed most of what I wrote just to repeat what you said. The biggest takeaway is that the tweet lied. Nobody's heights changed from last season to this season. So there's no "Why would the Spurs do this?", because they didn't do it. The author of the tweet used shorter measurements for everyone but Walker whom he mistakenly says the Spurs measured as being taller. My guess is those shorter measurements are actually true compared to the inaccurate ones the Spurs have listed historically. It could be a shoes-vs-barefoot thing, or it could be the Spurs taking height with a grain of salt as they've long done.
But yeah, assuming like eight guys in their 20s all grew is astronomically unlikely. Like I'd have zero problem calling the Spurs liars if they came out and said that (which they didn't, just as a reminder). No one of the team has any chance to grow except Primo, and that's not just because of his age but because they specifically said his growth plates are open. For most men, those close at around 16, so it's a rare thing for him to still have any chance at all of growing. Even with all of that stuff fixed, the odds of him growing are still low. Add in that no one else has been confirmed to still have their plates open, and there's no statistical basis for suggesting anyone grew. It happens. Famously Robinson and White both had growth spurts in college. Giannis and George both reported added an inch or two of height in the NBA after their rookie years. But there have been thousands of NBA players in that time, and getting four examples, or even multiplying it by 10 and saying 40 guys definitely grew in their late teens and 20s reveals the low odds of it happening. Raise that to the eighth power, and... Even generously saying 1 percent of NBAers grow taller early in their career, you still have 1/100,000,000 that all of those guys grew like the tweet said.