Activity 4, question 4. Interval vs ordinal scale of measurement doubt

[Inquisitive Learner]

The question says: Katheryn has recently read the booker prize winner “The Discomfort of Evening” by Marieke Lucas Rijneveld, and decided to rate this book on the Goodreads website. There she is asked to rate the book on a scale of 1 - 5. What kind of scale(s) of measurement is(are) being used here for rating?

The answer is Interval scale of measurement. 

I wanted to ask that what exactly we mean by 'scale of 1-5' here? If we take it as discrete values such as 1,2,3,4 and 5 then in such a case aren't we*rating* and simply the comparison is in numerical form(we know that we can numerically code ordinal scale of measurement's labels)?

So, how is it interval scale of measurement? In that case, how the difference would be defined between two consecutive values? Or  Is it that here, we are taking continuous values like someone could rate it as 1.5 or 4.7 or something so that it falls under numerical classification of dataset? I'm confused.