Where did you see the file names? If it was in the Title field of a Photos library the file may have been texted to you with that name. That long file name that you've posted looks like a file that was texted as I got this one not too long ago: 66942383451__231ECD9A-EC49-407D-81FC-171DE83B8E99.jpg. The system changes the name for whatever reason when it sends.
If you opened the library package and looked inside one of the sub-folders inside the Originals folder then you may have iCloud Library enabled. Photos renames the imported files to something like this:

to facilitate a more efficient comparison and syncing with devices using iCloud Photos. The original file name is added to the database and is shown in the Title field.When exported the original file name will be used for the exported file.
Photos that were originally imported into an iPhoto library before it was converted to a Photos library would have the original file name in the subfolder.
