Hardly overnight. Took him years of hard work and creating content to become accepted as some sort of authority to (some) people. Before that, he was just a guy putting out his opinion/experience to share with others. No different to being a forum member for years and sharing your thoughts and experiences.He started from a very honest and opened "I don't know how to cut and use a knife" and ended up overnight an authority on knives.
He definitely comes off as a bit of a shill these days, however for the most part he probably still sees it more as a hobby than a 'job' and is trying to be honest with his content.
Good luck to him - he reminds me a little of Chris (nightwing2303) who has been reviewing basketball shoes for years. Started as just a dude doing the occasional review to someone who was able to do his own collabs and start branding his own gear. I still watch Chris and think he remains very down to earth, more so than Ricky appears, however they're very similar in that their hobby has grown into a job - be it primary or secondary.