OK well, if you think his fish died in 24 hours because his DT is at 1.021, despite:
(1) he is keeping other fish in that salinity just fine,
(2) not only do many FOWLR hobbyists keep fish in LOWER salinity that OP's DT, but so do the most successful retailers (businesses that rely on keeping fish alive to maintain profitability),
(3) the disease forum describes how to safely treat fish with hyposalinity of 1.009 for 30 days (lot longer than 24 hours), and
(4) the OP said he drip acclimated over the course of 20 minutes. If the bag water was higher than that it should definitely be no problem. But even if bag salinity was lower, 20 minutes is plenty of time to acclimate up to the DT salinity, particularly since it probably was only off by around .003. Acclimating over a longer period than that only increases ammonia burn risk. (See Dr. RHF's question of the day on the subject) -
https://www.reef2reef.com/threads/reef-chemistry-question-of-the-day-12.173979/
I'm sorry but I don't see how your photos constitute sufficient evidence, let alone "proof". Nevertheless, I guess it's time to concede that continuing to discuss the issue with you is pointless.
For posterity, the reason vetteguy's opinion is surprising to me (in addition to the LA link above) is:
(1) Hyposalinity thread
https://www.reef2reef.com/threads/hyposalinity.247596/
(2) Fish arrive sick all the time, even from sources some people think are "safe". In fact there's a thread about that very thing on the front page of this forum right now. Also the shipping process isn't exactly gentle. Even outside of extreme temperatures this time of year those boxes often get tossed around. Easy to imagine how a fish could become fatally injured or stressed. Any of these are such plausible causes of death I just don't see the value in entertaining a hypothesis that just doesn't have very strong evidence supporting it. In fact there is plenty of evidence contradicting it.
That isn't to say it's a good idea to keep a reef at 1.021, but that's a completely different question than why did a new fish die within 24 hours.