First, for the law to apply, Trump would have had to demand that the NFL fire players based on their partisan political (i.e., party) affiliation. Trump didn't do that -- he didn't say fire all Democrats or even all Democrats that kneel during the anthem. And kneeling doesn't determine your "partisan political affiliation" -- presumably Trump would feel the same way about Independents, Republicans, Libertarians, Greens, etc. that knelt.
Second, the law only applies where the attempt to influence a private employment decision is made by taking or withholding (or threatening to take or withhold) an "official act" -- Trump didn't do that either.
Back in 2007, a United States Senator named Barack Obama suggested that CBS Radio had not gone far enough when it merely suspended Don Imus for racist comments he made. Obama's comments were lawful and in my opinion appropriate. Trump's comments also were lawful, but they were wildly inappropriate (like pretty much every single thing he says).