Have you ever seen it? 3.5″ Extra-High Density Floppy Disk, 4MB. If you remember, the most popular size has been 1.44 MB. 2.88 MB is also known, but 4 MB?
No, it is not a fake. It is one of many-many floppies, (more than 20), that were used to install software for Nortel Meridian PBX. Motorola and Mitsubishi were the only manufacturers for floppy drives that were able to read these floppies. Same floppies were used to backup/restore the PBX configuration.