If USB flash drive contain any of malware/virus/worm inserted to linux host without being mount (auto mount disabled), does malware/virus/worm will infect host
Longer answer: if a USB key is inserted but not mounted (as you mentioned) the system does not interact with it in any way, except to log that something has been inserted, so there is no way Linux will be infected.
Longer longer answer: if you insert a USB key, then mount it (for instance read only) the system will no interact or execute anything on the key unless you specifically start a program that is on the key. So it will not be infected either.
Since most viruses and malware are for Windows, you can therefore mount a USB key and start an antivirus program to clean your malware without risking the integrity of your system.
This is all true if it is a USB drive, but there is no way to know if it is a regular drive or something more malicious. If you dont know where a USB comes from, the safest thing is to just bin it.
OK, I agree it could be something more malicious, and that the safest solution is always to bin something unknown.
My position is that the op knows the USB device and suspects it has been compromised by connecting it to a windows machine. But the content may be worth salvaging. In that case, my advice still applies.