When to use a pair of 45° versus one 90°? Most in the construction trades work according to these guiding principles:
Use as few parts as possible, because handling more parts takes more time
Get the job done with whatever I have on the truck, because trips to the supply house and back to the job site waste time
With that philosophy in mind one would use a ...
...it looks like they didn't have a 90 and improvised...
Looks that way to me too. Ran out of 90s, didn't want to drive to the store.
There IS a concept of using a "sweep ell" instead of a sharp elbow in order to reduce the slight pressure drop that is created by the sharp turn, but that's generally insignificant in a residential system like this.
We can only speculate, and your guess makes sense. The usual reasons are:
To effectively create a longer-radius bend to get around something
To shorten the length of a run between pipes at right angles where space allows
Here we have no way of knowing.
A pipe wrench on the inside on this side of the threads to hold the indoor plumbing in position and a pipe wrench on the outside to unscrew the spigot should do it.
It doesn't look like there's any thread tape in there, though, so it might be rough going.
Additionally, it looks like they sleeved the copper pipe in something else to get it through the wall, ...