Well, one reason would be I was emailing my friends and family about the efficacy of wearing masks around the same time in March that the Surgeon General of the United States was posting on Twitter that masks don't work and the New York City Mayor was encouraging people to go to movie theaters and bars.

I don't think arguing from authority has a really great track record this pandemic.

The argument on the blog is pretty straight forward, and the data is all public.

Even among qualified people the ones that are so dedicated to the art of pontificating online that they feel compelled to blog about their ideas tend to also be the rabidly absolutist ones who's advice you should take with a grain of salt.

He isn't providing medical advice. Waiting outside vs inside based on simple statistics...

All else being equal, you're probably better off taking public health advice from a public health employee over a software developer.

However, if the software developer raises an admittedly good point based on specific, verifiable information (in this case sourced from covid19-projections.com, which sources covidtracking.com, which in turn aggregates data from state public health authorities) which questions the pre-COVID practice of observing a vaccine recipient for 15 minutes, their occupation should not make their point any less valid. This wouldn't be the first time that a well-established best practice turned out to be exactly the wrong thing to do given new circumstances.

The process of evaluating an argument should balance the informative value of the argument-maker's credentials without veering too far into gatekeeping or argument from authority (https://en.wikipedia.org/wiki/Argument_from_authority).

The medical field, or at least its public-facing portion, seems to be full of people who are reluctant to propose anything novel if there aren't rock-solid studies justifying it, even when it's clear (even to laypeople) that an analysis of the expected costs and benefits does confidently justify it.[1][2] It's a similar kind of thing to "no one ever got fired for buying IBM". And if you look at the incentives of medical spokespeople, do they actually suffer if they give bad advice? Is Dr. Mike Ryan still executive director of the WHO health emergencies program? His Wikipedia page still says so; its link to the WHO website has rotted.

Given that, it's precisely these guys, outsiders who think they're smarter (or less bound by rules or whatever) than those spokespeople, who are in a position to give us some of these important pieces of advice. Of course, that means you have to take them on evidence/argument rather than on authority. But it seems like the evidence/argument here obviously stands up.

[1] https://www.cnn.com/2020/03/30/world/coronavirus-who-masks-r...

[2] https://slatestarcodex.com/2020/03/02/coronavirus-links-spec... , search for "bungled its coronavirus response pretty egregiously"