Prosper did block one $20K outbound transfer to Kilen's bank account because of its size, though smaller subsequent transfers were allowed. (No further details were provided in the compliant regarding the procedures used with regard to the $20K attempted withdrawal.)
The whole episode occurred before Prosper began verifying ownership of bank accounts (rather than just using the deposit/withdrawal test to verify access to account information), and was probably a major reason for that change. I haven't opined on whether Prosper was derelict in its duties by not catching Kilen, only that it shouldn't try to give people the impression that it did catch him.
I do see two issues which might have caught Prosper's eye if it had been looking for irregularities in lender accounts:
(1) Transferring in from one account and out to another. (In Kilen's case, it was transferring in from two accounts and out to two others.)
(2) Leaving $80K sitting in a non-interest-bearing Prosper account while loaning out only $7K. (Kilen placed a total of about $30K in bids, IIRC, but I have no way of knowing how many were active simultaneously.)