Donald Trump famously said some uncomplimentary things about illegal Mexican immigrants, and promised to both build a wall to keep illegal immigrants out and deport those already here. As might be expected, many Mexicans whether resident in the U.S. legally or otherwise or in Mexico, didn't take kindly to these notions.
Coincidentally, or perhaps not, Trump found an organization to which he'd given his name and prestige - Trump U. - on trial in the courtroom of a judge of Mexican-American ethnicity. And Judge Curiel is not merely the son of immigrants, he is also to some degree an activist in support of immigrant rights.
Does any reasonable person believe the judge is unaware of, or indifferent to, Trump's pronouncements about illegal immigration? Would not a reasonable person believe the judge is likely to take a dim view of Trump and all he's about?
Given that, Judge Curiel appears to have a conflict of interest and should recuse himself but has not. Does Trump have a legitimate gripe? Yes. Does it make Curiel, as accused, "a hater?" Unproven, and likely unprovable.
Perhaps the larger question is whether people who choose to vote for Trump consider this matter an important issue, or not. My guess is they do not. His partisans are notoriously anti-PC, and charges of racism aimed at Trump reek of PC.