To be honest, that was ultra fast reaction time, but 100% of his focus was on the runby, the Baneling runby had already completed.
What I’m talking about is you have two fully formed armies and you micro on two front simultaneously. Maru did it about a year ago, against Dark I believe (after which MMM was the main culprit of Terran according to Batz). It was so beyond amazing to watch. I get why Maru doesn’t play like that any more (Terran players have real problems with their wrists), but damn do I ever miss seeing things like that.
Serral is truly impressive, but this particular bit of control is not what would make me think so. It’s his flawless mechanics and decision making I’m usually impressed with.