Is my biga supposed to be liquid?
To compare, I made exactly half that recipe, also measured in grams. It wasn't liquid, it was dough-like, but it was absolutely whisk-able. As a matter of fact, I only used a whisk to mix this. For what it's worth, I have a lot of trust in Paul Hollywood. I imagine this biga will be much more liquid in the morning. I'll let you know when I get up.

EDIT I want to mention too that I used 00 flour (Caputo Rosso red), filtered water and instant yeast. 

2nd EDIT As I thought I remembered, the biga loosened considerably overnight. It's now easily mixed with a fork. Not liquid, but much, much looser. And a bit bubbly.