if the line check was done before carrying pax, I would say that's unusual for jetalliance as line checks are generally not done.
And you know all of the JA fleet intimately......
But if line checks are done, they would certainly not be done on a training flight as that's just plain daft!! line checks and line training is done with pax. To do line training and line checks without pax is not the intention of JAR-OPS / EU-OPS.
For the operations I am aware of, all line checks, on new hires, are done without pax.
My tuppenceworth.