I'm not enough of a pitch design guy to elucidate it properly, but the Cubs made some changes to Soroka's fastball while he was on the IL, and PitchingBot on Fangraphs LOVES them.
Pitchingbot grades all pitches on the 20-80 scale. Prior to yesterday Soroka's fastball had a 52 grade, and his overall stuff a 43. Yesterday his fastball had a grade of 68, and his overall stuff a 58. Both scores are 10 points higher than any other individual game from him this year. This isn't just the velo bump from moving to the bullpen either. Soroka's fastball sat 95.0 yesterday, his highest of the season, but he's got several games just below that mark, including a 94.9 back in May.