Suggestions work by taking into account both videos you watch, other videos from that channel, but more importantly (higher priority) videos that other people watched after the video you just saw. YouTube wants people to explore as many popular and ad-revenue-enabled channels as possible.
When you get those random, dumb suggestions, it means the video/user hasn't had enough views for that suggestion system to kick in, so it just starts recommending generally popular videos regardless of what you actually want to watch.
I've seen this a lot. ADoseOfBuckley has only just recently (in the past 6 months) stopped doing this, and a number of other smaller LP channels I watch are still doing it.
