I'd expect top remains top.
For front and back of the same sheet.
I would expect the top to top but I would certainly provide a printed proof and/or call the printer to make sure.
...which way would you expect...?
Sounds like you're in the middle of learning a hard lesson in the universal print production principle; Never Assume Anything.
How many pages are involved? If it's a single sheet, like a postcard or brochure printed front and back, it can be ambiguous but I would expect the printer to ask if you want head-to-foot duplexing in such a case, and never do anything but head-to-head for more than a single sheet. It sounds like they set the printer wrong, and you should call them on it.
It is a single sheet printed both sides. So based on the comments it seem that head to head would be the usual way for it to be printed.
Thanks for the opinions.
You should designate the orientation when submitting to a printer whether it is "top/top" or "top/bottom" based on your document.