Hi shoota,
Your instinct is correct and the mechanic should be fired or worse. Outrageous what he did.. Do NOT ride it. Can ruin the crank or cause you a crash.

Need some input if you want to resolve it. You need to post a pic of both sides showing spacers and shims on each side Again do NOT ride it. The left crank arm is not properly affixed to the spindle which can cause a catastrophic failure and will ruin the crank arm to spindle juncture if you ride it.

You either need to remove a spacer or respace one side of the crank and/or remove the lash adjuster and replace with a wave washer and respace. Little time/money to get you back on the road safely.

Need to see two pics of spaces/mechanical preload adjuster if you have one. If you know if you have a mechanical preload spacer aka expandable lockring versus wave washer...let us know.

HTH