You can't really know that except for a few publicized ones. Those "transactions" you see are simply transfers. They "could" be a transfer to someone in exchange for USD. Or, as they are in almost all cases, they are transfers from one wallet to another both owned by the same person or exchanges that are holding large amounts of BTC moving money around internally as well.

To support your argument, according to this[0] the largest recent transaction about 3 hours ago was almost 25 million USD. 5 other transactions also exceeded 1 million USD in the last hour or so.

[0]: https://blockchain.info/largest-recent-transactions

I could be wrong, but I read somewhere that almost all of those large transactions are inter or intra exchange movements simply moving money around into different wallets. Also, they only indicate a transfer, it seems very unlikely that anyone has cashed out $25m all at once with bitcoin.

There's a VR webapp that was shared recently that shows live btc transactions. Just thought i'd share that for the 10 minutes I watched it the other day I saw numerous 10M+ transactions

Those are transfers, not necessarily transactions. No one probably traded 10m in bitcoin for USD. If an exchange transfers btc from one wallet to another for holding, it will show up on the transactions list.