It doesn't, really: the repeat starts with a "Repeat" and ends with an "END-REP," just like regular repeat syntax in Rule Machine. The "IF" is just part of a "Simple conditional action." What you're seeing is just a result of the fact that simple conditions appear on the same line as the action they are "attached" to. (It is a little odd that a simple conditional on a "Repeat" action acts as a check for the entire thing...but it makes things easy and is just something you have to learn, I suppose.)
Instead of this:
IF (Condition X) Repeat every Y
Do Z
END-REP
you could write this:
IF (Condition X) THEN
Repeat every Y (stoppable)
Do Z
END-REP
ELSE
Stop repeating actions
END-IF
...and they are exactly equivalent.
It's not "interpreting" things in the sense of looking at the pseudo-code you see on the screen. All Hubitat apps (of this kind, so ignoring things like service managers) work by asking the user to fill out inputs that get saved to an internal settings map (as in the data structure) for that app. In the case of RM, the inputs are things like devices and what type of action you want to run. Both what RM does and what it displays are the result of an undoubtedly complex set of app code that looks at the settings and devices what to do--but one of the reasons you'll see people say that RM rules aren't "code" is because they're not really. I will concede that what it displays looks a bit like that, and that you might consider it "programming" because it requires you to think like one--can't escape the fact that you need to know how things work, no matter how you do it. 
Given your comments, I don't think that the entry barrier to Groovy will be that high for you. I know it's not for everyone, but I think you might like it better in the long run given those same comments. Maybe come back to that possibility some day if you don't want to right now. I know lots of people would be willing to help you get started!
