Nope, i've been watching the video from this channel since a year a go with the same account that i use, but i didn't subscribe to this channel.Is this a new YouTube account for you? This looks like what pops up when you first open a YouTube account. I don't think it's something that particular channel setup. It's driven from Google to show a new user how to use YouTube features. I suspect this would have happened regardless of the channel you are on.
One way to test it to return to that channel and see if it repeatedly happens. I'm betting it doesn't.
Yep, already subscribed more than 4 channels, maybe you're right, it is supposed to appears in a newborn channel, maybe this stuff popped up on my channel by accident / bug...Are you subscribed to any channels? The only other thing I can think is that you've been using this account without subscribing to channels and YouTube is offering the suggestion.
This blue pop up is exactly the same when you first setup other google properties like Adsense, AdWords, analytics, etc. They show blue pop ups like that to teach you how to use the service. So, I assumed your account must have been new.
I don't know of any way for a channel to initiate a pop up for viewers to see. This had to be driven by google's assumptions about how you use youtube, trying to offer "help".