Could it be the tari kicking in? wasn't that going o be a bit eth style and assisting the Monero chain?
Tari will not add transactions to Monero. Will be or already is on testnet own blockchain. What will have incommon with Monero is that miners that mine Monero will also mine Tari. So secure both networks.
I believe most of the transaction volume growth is organic, however, this statement is not strictly true. The privacy features of XMR provide incentive for attackers to transact in an attempt to weaken the privacy. Lets not forget the IRS bounty on tracking Monero.
They would need to make a lot transactions. Also lets say two agencies want to do this attack. KGB and CIA. While one of them is adding transactions it is just making other agency work harder.