SYA Chart, page-1633

Just learning and have a couple of question if someone can kindly help. Please ignore my ignorance

During the day, buy and sell side was averaging around 65m shares on CommSec. If we had a huge sell off late in the day, why didn't the share price drop dramatically? I mean there must be a big and willing buyer who knew that there will be substantial volume on offer. This leads to the question that why would an unrelated buyer, with a knowledge of the selloff, buy at 29c as the sell off could drive the sp down by spooking the investors. Does this mean that the shares were traded between related parties and if so how it is likely to impact the share price in coming weeks?
2nd question: I read that only stocks approved by ASX can be short sold, I didn't find SYA on the list today? Can someone confirm if short selling is allowed for SYA.
Many thanks