It was burnt up. There was enough clutch material in the old fluid to keep it limping along. Once he drained it all out. All the particles went with it. Or fluid level is way to low. You need to drive it and see. If it is delayed engagement or If its slipping. Delayed engagement can be a improper installed filter or filter o ring. You can narrow that down by dumping an extra liter or two in it and drive it. Etc. lots can cause slipping usually it's burnt up.