Apparently they weren't smart enough to use a VPN, they were caught by a bot that looks for edits made by IP addresses associated with U.S. Congress. From the other article OP posted as a comment here:  CongressEdits, a bot account that for four years automatically retweets edits to Wikipedia made anonymously from IP addresses associated with the U.S. Congress, said the information was also posted on Mr. Lee and Mr. Graham “from US House of Representatives.”