Two things:

1. We read much faster than we speak, so watching a video is massively less time-effective. If the junior is doing this on company time, they’re costing money.

2. There was an article somewhere about a dev exhibiting these ‘symptoms’. Turns out they were barely competent. Their entire method was to copy code they found on the Internet, and paste it in. They were entirely incapable of writing code from scratch. The article went on to elaborate that, after extensive (expensive) coaching from the senior dev who authored the article, the person turned out to be a pretty good developer. They just started their career trying to advance by gaming the system.