I think that is the actual firmware (also for HSM 2) but it only just the communication between the USB port and the smartcard, and all the interesting things are in the closed source JavaCard applet installed by @sc-hsm on the SIM cards.
Maybe it is the cause of the performance differences you are seeing in Nitrokey HSM 2 - AES Encryption - Init/Update/Finalize supported? - #7 by Chesnet though - I don’t know.