Without knowing your exact state regs, I would say that what that means is that students who are achieving at grade level, but exhibit a severe discrepancy between aptitude and achievement, can also be qualified as special needs. Otherwise, under a pure RTI eligibility model, a student who has no normative weaknesses (at or above grade level in all assessed areas) can't be qualified regardless of their ability, because they are not dually-discrepant (significantly below grade level, and nonresponsive to tier 2 (or 3, in a 4 tier system) interventions). The severe discrepancy clause is intended to allow eligibility for students of high ability, who are underperforming, but still meeting grade-level standards.
It's not necessarily a short-cut to eligibility, depending on how your state has chosen to clarify policy. If there is a performance measure that is below grade level, you may still have to work your way through the eight weeks of RTI, to see if there is a general ed intervention that will bring the trend line on track to reach grade level. If there are no performance measures below grade level, then you might be able to move more quickly to the severe discrepancy stage of things. That might be aided by any data that shows asynchronous academic development, as above-grade-level achievement in one area will support the hypothesis that there is high overall aptitude.
