Never said you couldn't/shouldn't think that, just asked why you were surprised by it. Your reply makes perfect sense, it's a big jump from 247's ranking, which I personally put more stock into. But I also don't put as much stock into QB ranking for players who aren't even in their junior year yet. To me, junior year is when you start to see the truly elite QB prospects separate. The ones who have more than just physical gifts start to stand out.
Regardless, the difference between the 8th ranked QB (his 247 ranking) and 2nd ranked QB (his Rivals ranking) is often not much, depending on the class obviously. Let's circle back a year from now after junior film and camps between junior and senior year are complete.