Don't think the break formation shape really matters. The the bloke at the front shouldn't be looking for the bloke breaking behind him. The wingman should keep the guy ahead in sight. I guess he lost him, maybe saw someone ahead downwind, or looked at the wrong height. Either way, it must have been a bit tense jumping out at that height - and lucky it stayed in relatively stable flight.
We've done it too:
Aviation History from 1981. Browse historical aircraft from 1981 (article no 13)