It does look like it's compiled and linked with arm64 support as well:
$ file "Sadey\'s\ Sail" Sadey's Sail: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64:Mach-O 64-bit executable arm64] Sadey's Sail (for architecture x86_64): Mach-O 64-bit executable x86_64 Sadey's Sail (for architecture arm64): Mach-O 64-bit executable arm64
However, when I chmod 0755 the Content/MacOS/"Sadey's Sail" binary, macOS refuses to start it:
$ ./Sadey\'s\ Sail Killed: 9
Also, when right-clicking on the application and explicitly opening it, I get the visual confirmation that:
Apple could not verify “Sadey's Sail” is free of malware that may harm your Mac or compromise your privacy.
There is nothing I can do to remedy this.