Lost most data on SD card after moving it to another Android device

Yes, probably the SD card was formatted.
Try to plug your SD Card to a PC with an adapter and browse the folders to see if files are still there. I suggest you to configure Windows to show hidden files; it can be done from Folder Options.

If nothing shows up, they were deleted from the SD. By the way,
if they have not been overwritten yet, it's pretty easy to recover them.
Just use a data recover software such as Recuva

If you want to try with Recuva follow those steps after downloading and installing it from the official website.

1. From the Recuva wizard window, select All Files then Next>
   


2. Select "In a specific location", then Browse, then select your SD Card from the list (usually F:)
   


3. Check the "Enable Deep Scan" box then click on Start
   

The process may take a long time, depending on the PC's characteristics and the R/W speed of the SD card.
At the end of the process, you will be able to view and eventually recover files previously deleted from the SD Card.

edit: I suggest you to try both scanning modes as, in some cases, normal scan mode finds some files that are not detected in deep scan mode and vice versa