Heck, it could be that even large traders would ignore that and check 'No' in the end and the IRS wouldn't know, unless they are already watching some people who are getting some big gains on cryptocurrencies.
If they don't know already, you can safely assume the IRS will find out if you are using centralized exchanges to trade. Coinbase are in bed with the IRS. They not only hand over their customers' data, but they also give the IRS access to the blockchain analysis arm of the company (Coinbase Analytics). As soon as the government start putting pressure on other exchanges, just like Coinbase they will immediately fold and hand over your data. Exchanges are not your friend - they do not care about your data. They care about staying on the right side of the government so they can continue to be allowed to operate. They will sell you out without a second thought.
However, the fact that it's just a survey and they seem to be hesitant about using the term "cryptocurrency" to refer to bitcoin and altcoins means we have a long way to go before decentralized currency gets fully adopted.
A 1040 tax return couldn't be further from "just a survey". Their definition of "virtual currency" is such to include cryptocurrency along with other virtual currencies:
Cryptocurrency is a type of virtual currency that utilizes cryptography to validate and secure transactions that are digitally recorded on a distributed ledger, such as a blockchain.