Sounds to me like the screen simply doesn't work.
I don't think it has AutoRCM installed. If so, it would always boot RCM, even with the internal storage attached.
I believe what's happening is the Switch is booting when the internal storage is attached, but the screen doesn't work so you can't see it.
If the internal storage is detached, it's normal for a Switch to boot into RCM. And like you said, you can push payloads. But since the screen is dead you're not able to see what any of those payloads do.