Comey is worried that some notes or - god forbid - a recording of the meeting might turn up. Hence all the weasel wording. "I don't recall, there I may have said something like..." should be interpreted as "I absolutely briefed that in depth and was specific about it and I want to lie about it now but I'm worried I'll get caught so I'll suggest I don't really remember but maybe said something just so I'm covered if it comes out."
Trump sized Comey up pretty well. He knew that this turd would lie through his teeth if he thought he could get away with it but would be scared to do so if he thought there was any chance he'd get caught. That's why Trump tweeted that he might have recorded their meetings in the White House. That kept Comey from lying to congress.
Trump has known what Comey is since 2007 when Comey lied in order to usurp Ashcroft’s powers while Ashcroft was hospitalized. Comey was more than happy to do Lynch’s job as well.