[loopbit]

> As someone who's only touched Ruby for a few years

Well... Gemfile.lock has nothing to do with rails and all to do with Bundler, but if you've never used Bundler for dependency management it's possible that it's new to you.

But Bundler (and the Gemfile and Gemfile.lock) are one of the core components of rails, they even get mentioned in the getting started page (https://guides.rubyonrails.org/getting_started.html).

I only have a couple of years of experience with rails and haven't touched it in 6 years, but I'd be very sceptical of any article that tries to teach how to build projects in rails and doesn't even get those basics right.