If you want to argue that they should be held to a higher standard that’s reasonable but the way the comment was worded suggested there is some extra immunity for Congress. Which there isn’t.
what is the definition of non-public information in the context of congress and corporate "inside" information? If the congressional subcommittees get briefed on the Covid crisis or trade laws or policy, they might have advance knowledge that companies themselves don't have. Or if a company insider reveals information to subcommittees, is that actually making the information public?
Should there be even more strict rules for Congress than there are? Sure! But it’s not because they currently aren’t subject to insider laws.
That said, historically one of the things US* insider trading requires "breach of a fiduciary duty or other relationship of trust and confidence". Trading on material non-public information is not enough, there must be a relationship, there is a whole industry of people devoted to trading on material non-public information. They just have to get it without that breach.
So the argument for congress people (presumably, I'm not an securities lawyer) would be that most of the information they receive they do not receive via a fiduciary relationship or one of trust and confidence. Or that by Congress getting it, it becomes part of the public record. Though I can certainly see sealed/confidential testimony going the other way.
*This is an important distinction. In the US insider trading laws aren't about protecting the markets, they are about protecting shareholders. Its more about theft than market manipulation. European laws can have a completely different basis.