a) We do not trade gaps on their own. That is, we don't see a gap on Monday morning and simply enter a trade looking for the gap to close.
b) It's been said in here before that gaps often act as S/R. For example:
Forex Price Action
I read the NZDJPY article as well, and Johnathon did NOT say that gaps can be high probability trades; he said "gap closing trades can present high probability trades when they line up with support and resistance."..We look for gaps to act as S/R and that's what has happened here...
In the NZDJPY trade, the gaps lines up with S/R and then a pinbar was formed. There's nothing new here.
(i) Gap = S/R (key horizontal level)
(ii) Pinbar = PA signal
Hope that explains it. I know when Johno comes back in, he'll tackle it as well.