Load the new image in either the Loupe view in the Library module, the develop module or select it from the Grid view in the Library module before you go to the Print module.
Did you actually print that other image to a printer or to File?
The film strip is just that, like you are looking at a strip of film. Selecting something in the Film strip area doesn't always do what you think it should do.
I didn't print or file the unwanted file however I had viewed it in the develop module.
The image I wanted went from loupe view into develop module and the I selected the print module which displayed the unwanted image.
I removed the unwanted image from the library (not from disc). The print module then loaded the next image in the sequence from the film strip.
I finally had to remove all the images from the collection accept for the one I wished to print.
Do you have the Tool Bar showing in the Print module?
In the Tool Bar do you have Selected Photo selected in the "Use:" area?
Do you have Single Image / Contact Sheet selected in the "Layout Style" area?
Have you by chance selected "Create Saved Print" and is that Saved Print selected in the Template Browser area?
I just did a test with several images. Every time I selected a new image in the library module then moved to the Print module and in a Snap the image changed from the previous image to the new one I had selected.
Hadn't set selected print in the bottom tool bar it was set at film strip. I'll put it down to old age.