question about placing windows in the foundation

If the home inspector is the building inspector from your town or city he should know the building codes.

You said your wall is a poured wall. It should have a grid work of rebar in it
Vertical and horizontal. The horizontal rebar should strengthen it across the top of the window like a lentil. If it was a block wall you would use a lentil because most of the rebar runs vertically through the void of the block.
The block does have anything to hold it up.

Here's a little picture. I did a little editing of it for reference.
g01700art01.jpg
If the company you are having install it do this all the time you'd think they should know what they are doing. Of course that's not always the case.
If you still have doubts get a hold of the town or city building department to find out the building code for this type of project.