Perhaps not worth of your time, which is precious for TinyCore development, but eventually it would be interesting to dig to the bottom of this and find out what is responsible for not booting in Zip emulation after TC usbinstall...
Just as roberts precisely explained, as much as we have standard for CD booting, there is no standard at all for usb booting and depending on BIOS and usb stick it can behave wildly different... This is a pity, because usb is common nowadays but manufacturers never came together to set ground rules...
To be honest I haven't seen such variations in USB boot. Machines around me booted from USB without any issue. There were many different machines including ...books like Asus, Acer, IBM, Lenovo, Dell, ... as well as desktop machines with different BIOS and from different vendors, like MSI, ASUS, GIGABYTE, ...
My long time favorite for years, SLAX booted always fine from USB stick configured with its own WINDOWS or LINUX installation tool.
Or in case of old machines it was not possible to boot at all.