The first time Sonic went Super in Road Trip wasn't exactly as stunning to Tails as other au's and stories.
Tails is like maybe 5 here (I'm not actually that organized on the timeline for this au yet, I'm getting there though, things are getting in order.) and he wasn't forced to grow up and be a hero in this au. So he's a bit more childish than canon Tails because he doesn't feel as pressured to mature and grow up fast. Plus, he genuinely thinks Sonic is going to die and this is the last time he see's him, so tears are bound to come down.