At many companies (I want to say most), Redis is seen as an actual durable production database and operated that way, not just as a cache that can disappear at any time. It's not unreasonable for a new dev to assume this unless told otherwise.
Ultimately though, regardless of whether you’re experience is true for the wider industry or not, if you’re letting a junior dev who refuses to read product documentation the responsibility of architecting production systems, then your problem isn’t Redis.
Also, because it's so easy to setup, most DevOps/SREs/Ops just chuck into production without reading about which flags to set because we are not informed it's a requirement until 11th hour.