Those blocks are most likely from an actual retail account. (Sorry if I've posted this here before.)
I was on another board a couple of years ago, and a poster said that it was their trades.
Don't remember for sure the type of account, but it was something like a Retirement Acct. or something other than what we are mostly using, that only allowed trades under 10K to be done on-line. If 10K or greater, they had to call in and speak to someone.
So they just keep repeating their orders until they were full.
There was no indication for me not to believe them.