Noice I been thinking pretty much the same thing!
I believe that Guaido was head of National Assembly which is the legislature? Due to the suspicions that elections were illegitimate both the Presidential one recently and the Maduro instituted and Maduro friendly legislature elections, the next in line if no President would be Guaido. Confusing, but this article talks about it. https://www.nytimes.com/2019/02/04/world/americas/venezuela-maduro-guaido-legitimate.html