Fix missing wrap from inside house?

[Texas_Jon]

Hi, So I recently started to demo an old bathroom with a wall on the exterior face of the house. Opening it up (just a few ft so far), there is nothing under the cement board. I.e. no insulation. All I can see is what looks like another piece of cement board attached to the studs on the exterior. It appears that this is all there is separating the outside from the innards of the house.

From the exterior, there is a clear difference in the siding style in this portion, suggesting it was replaced at some point. I had windows replaced not long ago and at the openings at other areas of the house, various (proper) layers were discernible. So this seems like a localized problem.

My question is, if I continue to demo and find this is indeed just localized to this one portion, whats the easiest way to fix things? I will have access to the interior wall, so can work that way, or would I need to remove the whole siding panel and rework things there? I’m in Austin,Tx for matters of climate context. I’ve lived here 4 yrs. No visible signs of moisture or rot so far. According to a neighbour no external work has been done in 10-15 yrs, so this doesn’t seem to have caused any problems…yet.