Errors per LOC is allegedly constant, across all languages.
I also consider the cost of change when designing things.
I once created an HL7 wrapper that was a marvelous thing of beauty. Fluent API, clever use of the type system. But no one could maintain it, including me. It had too much magic. So I scrapped it, went with a dumber implementation.
If this is true, then a more verbose style will have a higher error rate. (more LOC to do the same task -> more errors)
I think that's what he means.
This implies that more expressive languages(more expressions per line) are less prone to errors.
You conclusion would be correct if he had stated that error per expression was constant between languages.
Well, there is some truth to that. Anecdotally, most lines of code will be read many times before they are changed/discarded, and most of this reading will be skimming, where the reader is either: 1) trying to understand the structure of the code, or 2) trying to figure out where to make modifications.
Code that's hard to understand quickly (e.g. by skimming) is technical debt. I think a good litmus test would include not just the effect on error rate, but also the effect on the time it takes to understand the code and to make changes to it.
w/r to Python in particular, it has a history of ending up with idioms that are "tricky" and not particularly more or less terse than other techniques, but are able to exploit the standard library functions to get a faster-running result.
This is, of course, at odds with the motto of "there should be only one (obvious) way to do it," so every experienced Python programmer has to internalize a small dictionary of idiomatic one-liners for these exceptional cases. (Fortunately, it's not that big. I can only think of three or four off the top of my head.)