I am not using Telegram and wouldn't have used it if I was a US journalist working on something potentially dangerous, but I don't think this is a good argument.

As long as Telegram isn't compromised by USA-allied countries (Iran is somewhat allied with Russia), it might be a safer choice than Signal for US journalists. The reason is that USA can easily send a letter to Google that would reveal a lot about that person + they have root on the device.

Just like the safest place for Snowden right now is in Russia.