If you visit the software update page and download the GCD file and open it using RGN_Tool,
it would show that the GCD has internally HWID 1749 and version 4.50.
This HWID has always belonged to nuvi 65/66, while the HWID of nuvi 67/68 has always been 2088.
So it looks like nuvi 65/66 firmware version 4.50 software update was assigned to nuvi 67/68 firmware version 3.50 by mistake.
To confirm this hypothesis, let's compare both GCD files and see that they are equal.
UPD: sorry for posting on a wrong subforum
