It appears that YouTube is testing a new gesture on its Android app, that is going to allow you to swipe from left to right to switch to a new video. This is something that Google+ user Joe Kelly found on his installation of YouTube and was able to do a screen recording of it - which is shown below. Basically if you swipe from left to right you can switch to the next video in the playlist or in the recommended list that appears below the description on YouTube pages. This feature, currently, is not available to everyone. So it appears to be something that the YouTube team is testing out.
This gesture would make it easier to switch between videos, if you are looking to jump to the next one rather quickly, though it appears to only work when the video is not full screen or in landscape. Perhaps adding this to the landscape view would make it even easier to jump forward to the next video, as you won't need to rotate your phone to jump to the next video. It's a pretty interesting feature for the YouTube team to be checking out on the app, and potentially putting into the app in the near future, it's going to be interesting to see how many people are actually interested in using it.
YouTube and other teams at Google, are always testing out small new changes to their apps. Google is pretty well-known for testing out new updates to Google+, Google Search and many other Google apps, and some of those changes never actually make it to the app for everyone to use. This could be due to a slew of reasons, including feedback from users that did get the feature on their installation of the app. So it's not surprising to see YouTube testing it out and trying out new features as well.