It's BS. Rasmussen has always overinflated Trump support from black voters.
"One week before the 2018 elections, Rasmussen had President Trump's support among black Americans at 40 percent. According to exit polls, only 8 percent of black voters nationwide voted for Republican candidates."
"Gallup averages show Trump with a 10% approval rating among blacks in 2017, 11% in 2018 and 10% so far in 2019."
Another poll in October showed him with just 7% support.
I can easily see 34% of black voters being in favor of Trump. Since Trump denies the man-made climate change, he has obviously nothing against coal mines, unlike those people who consider fossil energies bad. Trump's base strikes me as the kind of people who do not regularly bathe, so those people who work in coal mines can easily qualify as black even when it's not their native skin color.
It's a matter of methodology.