Fedora boot screen shows both Fedora logo and Lenovo logo. Why and How?

This is the result of Hans de Goede’s work on flicker-free boot in Fedora. Hans developed a new Plymouth theme which takes the firmware bootsplash and adds the Fedora logo to it, until boot finishes and the desktop environment takes over.

This works because bootsplash logos are now exposed as an ACPI resource, which you can see in /sys/firmware/acpi/bgrt on systems which support this.

See also the flicker-free FAQ. (This also explains how to modify the Plymouth theme so that the logo is still displayed along with the disk decryption password prompt.)

Thats the new Plymouth theme. You can easily change the theme using

plymouth-set-default-theme --list
plymouth-set-default-theme <one from list output> - R

Source: https://fedoramagazine.org/howto-change-the-plymouth-theme/

On a very low level, the video memory is not automatically cleared when it is written to. Unless Fedora boot process explicitly clears the screen or changes the video mode, whatever it puts on screen will appear "on top" of what's already there.