There is a real risk in applying power to the jump terminals when the battery is disconnected.
Where is the battery positive terminal?
If you only disconnected the negative terminal, then there is no real chance of a problem.
If you have completely removed the battery or only removed the positive terminal, where is it sitting? If it is touching the chassis or the negative lead,
Bad Things (tm) will happen if you apply a high current source to the jump terminals....
