Triangle Face a bounty hunter was tacking Dr Evanzen and Walrus Man before Jyn Bumps in to them…
This probably allows the two criminals to escape as Triangle face is caught the other side of the Hover Tank and has to wait then the battle kicks off allowing Dr Evanzan and walrus face to evade capture.
He may have been going to shoot just as Jyn bumps in to them or does he bump in to Jyn to cause a diversion.