No Rivals bases it on an exact school, and has nothing to do with the offer list.
If a Rivals recruit was listed at let's say a 5.9 and 4* and in June, 2017 he committed to Nebraska over Alabama, USC, Texas, Ohio State, Michigan, Auburn, UCLA, Penn State, Florida and Florida State. Rivals would still downgrade that recruit to a 5.8 level, and won't take into account the offer list.
Now if that same recruit had offers from Minnesota, Iowa, Wisconsin, Arizona, Duke, Boston College, Mississippi State, Rutgers, Missouri and Vanderbilt the same thing would happen.
Switch it up here and let's say the recruit commits to USC instead of Nebraska in June 2017. He will most likely end up at 6.0 and 4*
Rivals don't care about the offer list they care about the school they commit to
Explain Jurgens then? He was a 3* and now a 4*. LSU offered and he took a trip. He went up to a 4*?