Hmmm, not sure what would cause that. But I wouldn't worry too much as long as the plant itself is doing well. Sounds like you will have a couple dozen replacements pretty soon. Maybe it just set too early and the plant decided to give up on it and concentrate on maturing a bit more before growing it's peppers.
Bruce

Some insect could've gotten inside and started doing it's thing, but I lean towards sunscald. Especially since you said it didn't have much protection and Poblanos are a thick fleshed pepper(which tend to develop sunscald easier than others).

Is there a hole in the fruit that looks like an insect bore through?

Kevin

The first pod or two are often deformed and mishappen + poor flavor, i almost always yank them.

As for that brown spot, it can be caused by at least 4 or 5 different things, i wouldn't sweat it just yet especially if the plant looks healthy and surprisingly has around 40 flowers ?! Just be careful not to add a high nitrogen ratio at this point, otherwise a lot of your blossoms will drop.

Kevin, no insects. The pod looked fine except it was small and severely burnt on top. I cut it open, and it wasn't rotted on the inside. Sunburn seems most likely, I guess.

@sjetski, thanks for the heads up on the nitrogen!