To be fair this tweet doesn't say anything about training data but simply that it theoretically can use present day data if it looks it up online.

For gpt4 i think its was initially trained up to 2021 but it has gotten updates where data up to december 2023 was used in training. It “knows” this data and does not need to look ut up.

Whether they managed to further train the initial gpt4 model to do so or added something they trained separately is probably a trade secret.