My takeaway is that Mueller didn't want to say, or be interpreted as saying, anything that was not in the report, period. He wasn't going to opine, judge, explain, nor extrapolate.
The Dems wanted to get him to say that impeachment should be on the table. They also wanted him to take things stated in the report a step further and character them as criminal.
The Repugs wanted him to say that Scrotus was was not indicted because he was 'cleared' of any wrongdoing. The Repugs also wanted to push the narrative that the team Mueller put together were all Democrats and all wanted Scrotus out. In other words, that they had an 'agenda'.
Neither side got what they wanted. But both sides will be able to get 'something' out of what he said.