The type of remote control used often depends on the device category. Streaming devices such as Nvidia Shield, Apple TV, and Roku typically utilize RF (Radio Frequency), whereas TVs, AVRs, and DVD/Blu-ray players tend to rely on IR (Infrared), although exceptions exist. Many devices that come with an RF remote still support IR functionality. For example, my Apple TV includes an RF remote but also supports IR. To date, I haven't encountered a TV that lacks IR support.
Regarding the OMSC remote you mentioned, my suspicion (though it could be incorrect) is that it registers as a keyboard when connected, similar to numerous other comparable devices. Certain companies specialize in crafting customized remotes for entities like OSMC. Thus, it likely transmits a combination of media key presses and other keyboard shortcuts when its buttons are pressed.
Ben