1 thread would have been enough for your questions.
Does someone at work have access to your "work" google account?
Let's rule out a couple of things here:
1 - You were browsing from your personal iPad, so no one at work has access to that device. They aren't going to pull data off of it.
2 - You were not browsing from their network, so they won't have logs if they have something doing monitoring and reporting on web browsing.
If your boss or someone else at work has access to your google account that was used, then at some point they did have access to your Youtube history. If you deleted your Youtube history, then they might not have access anymore. I don't know much about youtube account privacy settings.