“It's a poster for one of my earliest experiments... doesn't work though, complete waste of time.“ This page refers to content that existed in earlier versions of the game, but was eventually removed or repurposed.
10AV is the eleventh FMV in MediEvil. It is identical to 9AV, but ends a lot sooner. It's not used anywhere in the game.
It can be presumed that this FMV wasn't just meant to be a shorter version of 9AV, but instead a different FMV altogether - the 9AV FMV is only played because the 10AV file is missing from the disc.