I don’t know why the crane was staged so far away. I have used cranes many times on jobsites and they get as up close and personal as they can. Maybe the crane was set up over there and they asked him to lift this one little thing and instead of moving he just took a risk and did it. When he was so far away like that it doesn’t take much weight to tip it.
On a site like this, that crane is used mostly for area wide lifts of mostly light weight items like a pipe or beam in the lay down area that is shown. That is also not a giant crane. Definitely operator error, he should know his boom length, lift weight and use corresponding charts inside of cab showing maximum boom angle.