I tried Photoshop CC 14.2.1 on Mac and a greyscale image looks like a greyscale image, not red. Here's an official greyscale image you can try out.
If you use ProEXR EZ, there's this ProEXR File Description that will tell you exactly what's in the file.
Maybe your file just has a red channel and Photoshop opens it to full RGB. Then when you save you have two extra channels which Maya is interpreting. Copying red to green and blue still might be a good fix.