To be honest, I think I've made episodes of my comic in two different ways:
First dialogue then create drawings that would suit that dialogue. And then my other method because sometimes I just like to draw first. I draw panels while the dialogue kind of develops either while drawing or after drawing...I think the second method is kind of similar to this that you're describing but my comic has an overall story so it doesn't fit the bill completely. I don't think I've ever just made or found a random blank panel/page (that doesn't connect to anything) and just challenged myself to make-up a story about it. It's interesting though, so like I said, I kind of want to try ^^
Both methods work for me, actually, it's kind of fun to create the comic with different methods. I think I've also seen a creator do this for their fans, offer a panel that has bubbles of dialogue to their fans and see what dialogue they come up with. It's usually funny but it can be a bit dangerous considering how the internet is xD