Besides the gauge wire undersized how would you write up this jumper?
This is a 200 Amp sub panel commercial.
3 phase Panel Needs immediate replace with Correct Panel .
Recommended Upgrade by qualified person
The 3 phase panel would be common in a commercial setting. The supply seems to only be two hot legs instead of three. This may be a three phase panel being used in a single phase setup. To avoid 1/3 of the panel being dead someone added the jumper to supply power to the 3rd leg.
While the 2 conductors in the lug is improper, it is hard to make any other assumptions as to what is happening.
The ground wire to the can may also be using a screw that does not have the 2 threads of engagement required.