To arrive at the answer to your primary question:
Was Windows installed in UEFI mode?
Open the System Information app from the Start Menu or issue the
msinfo32 command from the Run... dialog (WinKey + R), a Command Prompt or a PowerShell terminal. In the System Summary pane, which is shown by default, look for the value of the BIOS Mode key.
- If the value is UEFI, the answer is yes.
- If the value is Legacy, the answer is no, Windows was installed in BIOS mode.
To the question of how you control the type of Linux installation you perform, you were correct when you asked if it was determined by how you boot into the contents of your install media, be it a USB flash drive, an optical disc (CD/DVD/BluRay) or a networked install via PXE.
The presence of multiple entries in your Boot Options menu targeting the same device, with one specifying UEFI, was the point at which you committed to the mode the installer would use going forward. It has nothing to do with the contents of the medium (which is why you didn't need to pick a method when you downloaded the image file from which you created it) as the installers for all major operating systems include executables for both methods.
When using a solid state medium such as a USB flash drive or memory card of some sort, the method you used to write the image to the device does determine whether it will operate in UEFI mode. The UEFI specification requires the existence of a separate partition to hold the bootloader or the presence of certain flags to be set in the GPT (GUID Partition Table) if the entire contents of the image are placed in a single (FAT32) partition. Going forward we'll assume that you were careful to select a method that offered to create a UEFI-capable drive/card, such as Rufus on Windows or WoeUSB on Linux.
The potential for the two different outcomes with UEFI arises from the inclusion of a Compatibility Support Module (CSM) which causes them to behave like a BIOS would and be detected as such by the operating system. This is what produces the non-UEFI entries in the Boot Devices menu and is usually labelled as "BIOS Compatibility Mode" or "Legacy Mode." In the event a computer shows only one choice for a particular drive in the Boot Option menu triggered at startup, it is necessary to restart the computer again and instead press the key to enter the firmware settings (often still called BIOS Setup) and find the entries that control the Compatibility mode and either disable it entirely (UEFI Only mode) or set the configuration so that it will attempt to work in UEFI mode first and only if unsuccessful, fallback to BIOS/CSM mode (UEFI First mode).
In conclusion, I'll make note of the fact that current best practices regarding dual-boot setups almost always dictate that whatever method was used to install the first operating system on a computer also be used for the additional ones that are subsequently installed. I mention this to point out that the decision on which mode to install your Fedora environment under was, in essence, decided when you or the manufacturer performed the original Windows installation on your computer.
The reason is that to use operating systems installed with different modes on the same computer requires (at best) using the Boot Option menu every time you want to access the OS using the non-default mode, and more commonly involves changing the firmware settings to switch the bootloader mode entirely each time you switch your OS. This is in contrast to the various menu options available in UEFI (rEFInd, GRUB, even the Windows Boot Manager) that cause the computer to stop and present a menu at power-on listing the available operating systems (example of rEFInd below) and booting into the one that is selected.