I would be willing to bet it had nothing to do with your knowledge in React but probably more about something stupid like you didn't use a certain library they like or maybe you didn't do things 100% in the latest cutting edge React way. It's all nonsensical. As you said, there are far too many factors in which you couldn't possibly prepare for or do anything about. An interviewer could simply be in a bad mood that day, or maybe they don't like your shirt, who knows. It's really not worth even caring about.
I know for sure I've utterly failed code tests before, like when asked to solve a graph problem in 15 minutes back when I had very little knowledge of graph algorithms.. but still, a lack of knowledge does not mean a lack of motivation, a lack of intelligence or a lack of skill. I've failed to get hired at companies where I have friends working who have told me that I'm a better developer than a lot of their coworkers, but because I simply was lacking in a certain area, I was dismissed without a second thought. It's easy to sound like a poor loser, but the reality is, not everyone knows everything and I think sometimes it boils down to luck more than qualification.
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I would be willing to bet it had nothing to do with your knowledge in React but probably more about something stupid like you didn't use a certain library they like or maybe you didn't do things 100% in the latest cutting edge React way. It's all nonsensical. As you said, there are far too many factors in which you couldn't possibly prepare for or do anything about. An interviewer could simply be in a bad mood that day, or maybe they don't like your shirt, who knows. It's really not worth even caring about.
I know for sure I've utterly failed code tests before, like when asked to solve a graph problem in 15 minutes back when I had very little knowledge of graph algorithms.. but still, a lack of knowledge does not mean a lack of motivation, a lack of intelligence or a lack of skill. I've failed to get hired at companies where I have friends working who have told me that I'm a better developer than a lot of their coworkers, but because I simply was lacking in a certain area, I was dismissed without a second thought. It's easy to sound like a poor loser, but the reality is, not everyone knows everything and I think sometimes it boils down to luck more than qualification.