I'm pretty sure it's an actual cel.  I believe it
says in the description that it is not attatched
to the background.  A lot of people will purposely
not show the sequence numbers for security reasons. 

Here's the Babel Fish translation :

Whether ? ? of plain clothes form of the
background < Size B4, it is not stuck > It is the
attachment cell picture. Animated picture has not
been attached. Old it is and being to be the work,
being secular fit state please consider. Overseas
dispatch is not possible, also self introduction
viewing. * Reference: The studio ? obtain; The
original spring which it waits; Crane wide seeing;
Aikawa ? ??; Akemi Takeda; Boy jump