This is a stupid poll for several reasons:

First, the total percentages add up to much more than 100%
Second, Trump's disapproval rating of 55% is nothing to cheer about since that's what Obama had when he left office.
Third, even though the disapproval rating of Congress is 66%, you're comparing apples to oranges with Trump (1 person) vs. Congress (535 persons) as Congress has had a tougher and more complex job to do than Trump has had so far. 
Fourth, Congress isn't tweeting at all hours of the day and night or holding pep rallies for its known supporters across America to bolster its image and its egos.
Fifth, Congress has never been popular with the people.

But, most critically, what the Hell does a nebulous concept such as "Approval" really mean?

It is not the same thing as asking someone to judge the competency or effectiveness of a person or body of persons. It's more akin to a popularity contest than any serious inquiry into the actual work being done in Washington.