Just gotta remember there's nothing special about there being an assignment there, it's just another expression. `if` is another expression and it doesn't care about the status of assignments or whatever is in the conditional clause, only what the expression inside evaluates to.
As far as the assignment operator evaluating to the right hand side, it'd be more difficult to understand if that wasn't the case. There are more scenarios to destructuring on the left hand side than the right.
Also keep in mind there's no such thing as a "failed" assignment. They always work, sometimes things are just assigned to nil explicitly or implicitly.
This case is somewhat hard to get because it brings together a few things of Ruby in way that can get weird. Those things separately are actually pretty good, but bunched up makes it a bit more dense semantically. Which is why it's best to avoid getting too clever with assignments in conditionals.
