It doesn't. But the VRA says they must be represented by "the candidate of their choice", whether he is Hispanic or not. Whether they can elect the candidate of their choice depends on their share of the electorate.
Note that an Anglo represents a Latino district in Houston and is considered to be the "candidate of their choice" while a Latino representing a half-Latino district in San Antonio and West Texas apparently doesn't qualify because only Anglos vote for him.
SCOTUSblog has corrected itself to say that it was Bonilla's TX-23 that was struck down and that Frost's redrawn TX-24 was upheld. That's more like what I expected!