The prediction was that for the 2024 U.S. presidential election there was roughly a 50% chance Joe Biden would be on the general-election ballot and a 50% chance Donald Trump would be on the general-election ballot.

What actually happened:

• Joe Biden was the Democratic Party nominee and appeared on the 2024 general-election presidential ballot.
• Donald Trump was the Republican Party nominee and appeared on the 2024 general-election presidential ballot.

Both Biden and Trump were in fact on the ballot, so ex post the realized outcome was that both appeared, not that each only had a 50% chance of doing so.

While you can’t strictly falsify a probabilistic statement from a single outcome in a formal statistical sense, for the purposes of judging this concrete, binary forecast about who would be on the 2024 ballot, the world that occurred ("both on") is inconsistent with the implication that it was only a 25% joint-probability scenario (0.5 × 0.5). Treated as a practical prediction about who would run, it did not match reality.

Therefore, evaluated against what actually happened in the 2024 election, the prediction is best classified as wrong.