He has high sens, that's why his rifle jerks a bit, not really much to do with pressure. Even without pressure, his rifling is a bit janky, but unlike Kjaerybye, his aim's on point most of the time. This was bad decision-making, and being a major semi-final, it just adds to the anxiety.
And s1mple won another 1v4 clutch in the next match against ENCE on Inferno. Zywoo hasn't even made it beyond quarter-finals in any major, so your comment is bullshit. In regular match-ups, s1mple pulls off 1vX clutches in every match. s1mple hard-carried an NA team to major finals in his 1st year itself (2016), and also made the iconic graffiti play. Zywoo's best performance in majors has been getting knocked out in quarter-finals, and getting knocked out in group stage. So, show some respect. It doesn't hurt. You don't need to pull others down to pull your idol up :)