No, he doesn't have the "#1 transfer portal ranking".
Read the ranking system description: "On3's Team Transfer Portal Index utilizes the On3 (P)erformance score to measure a team’s production during the transfer process, compared relative against its roster and not a comparison against other schools. This proprietary algorithm determines if a school has improved its overall team talent, stayed the same, or declined in talent during the transfer window."
In other words, they have the best transfer portal class in terms of improvement to their existing roster as determined by On3. Which ultimately isn't saying much. It says the kids they got are expected to be better than the kids they ran off and by this measure of "improvement" they gained the most ground. So, talent wise, they probably still suck but they suck less than they did by whatever metrics On3 uses.
But in sheer numbers, I would even doubt that to be true at this point. Unless the rest of what they get in the portal turns out to be REALLY, REALLY good, they very likely aren't to have gained much or certainly not enough to move the needle in the short term. They got a good QB and a 5 star WR neither of which has played a down of FBS football. The rest of the transfers are largely unremarkable.