F11 can't be what "synced up" the runtimes because the floating props predated that. Called out: ILF 32:03 "I think this is where all my props have been going... if all the games have been connected for a while... but that was happening before I pushed F11, so... has everything been synced up the whole entire time?"
Connections
F11 is the "switch to TF2" key in SFM. Toggles between game and editor; tf2 runtime and sfm runtime linked