All fish live in a soup of microscopic organisms. If you do regular water changes, gravel cleans and filter maintenance, the fish will be healthier but there is no guarantee any fish from anywhere is free of all diseases.
The fish looks ok in the pictures and might not have any diseases. But it could still carry a disease into your tank.
Personally I would just move it into your tank and add some salt. (2 heaped tablespoons of salt per 20 litres of water). Keep the salt in the tank for 2 weeks and they should all be fine.