This also allows the app to run seamlessly on a USB pen stick/harddisk so you can use it on different computers without fuss or being tied down by an installation. The app stores all it's settings etc in a folder alongside the EXE itself, usually "(app name).exe_storage", and automatically manages any references to external filenames/folders on it's own disk drive, allowing it to operate on different computers that might assign its disk drive a random/different drive letter without interrupting access to any referenced filenames/folders.
And no, it's not multi-platform/cross-platform. It's a Win32 (32 bit) binary/codebase. The occasional experiment I have done in the past into cross-platform coding has left me less than impressed. Unfortunately, I'm used to coding at the low-level/API level, and as soon as the programming language starts to abstract away the commands things tend to get dicy for me, and I inevitably find myself lugging around 20+ MB libraries of converted functions, and with no particular guarantee the final app with behave or look similar on different platforms.
Though I do wish such a thing existed. Something like a universal translation layer for all variations of software apps that is hardware accelerated and uniform in execution down to the very last and simple command would be a dream come true. Can't see why in 2025 we are still expected to code and/or compile apps for different operating systems and hardware platforms.
It's quite clear they mean more a (much) stricter variation of the "no installation" definition than the "easily buildable on other OS" definition. Though they do mention execution under translation environments as a requirement.