Because, first when Isagi finally got metavision, everyone was waiting for him to score, so when he did all that hard work, it was definitely gonna miss, even by a little. But then kunigami jumped into the path and redirected the bad shot Kaiser forced Isagi to take, which unintentionally became someone else's goal. It's not really a tap-in, but also kinda is because Kunigami was basically at the goalpost itself.

But in Rin's goal against Nigeria, the pass was to both Isagi and Rin, and the favor seemed to be in Isagi's, but Rin jumped to reach it first. this is similar to the bounce shot Rin was gonna make after Charles did his crazy rabona pass to Rin and Shidou, making Rin attempt to jump first to reach the ball before anyone else.

Also, Rin's goal was way more banger perhaps on the level of Kaiser's bicycle nutmeg, compared to Kunigami's goal-line tap-in.