I dont belive that claim is actually true?
the most likely result predicted by 538 was 312 for trump [0]
the issue with the model was the 2nd most likely result was 319 for harris.
they thought the odds of a recount being decisive was around 10%.
That hardly seems evidence of "predicting a split election". which prediction are you thinking of?
[0] https://projects.fivethirtyeight.com/2024-election-forecast/