Hey,
i just had a few minutes left, searched around a little bit with the forums search on the top right and found the following thread below which seems to have discussed this topic thoroughly.
If i understand the whole thread correctly my assumption seems to be correct and the QNAP devices are not shipping a recent version of this libxml library required by ownCloud. AFAIK such libraries are included in the operating system so it seems to me that it is up to QNAP to update it.