There is more than SSS to go on here, if you saw his at bats.
1) Seattle clearly had a plan and was relentless with it.
2) He was unable to make any adjustment and got beat on sliders in the zone.
3) On a positive, no Javy Baez here, his discipline on the sliders is excellent.
But the core is they attacked him that way daring him to prove any level of competency to the contrary, and at least for four days, there was no adjustment, no competent swings with bad luck. Maybe it was just respect of his ability to hit a fastball and a bad weekend, but it did not look that way. He seemed mechanically off on every swing on a slider in the zone and looked really helpless.
I think the statistical outcome of four games is almost completely meaningless, and I'm not at all worried about Story, etc. But the substance behind those outcomes for Casas are concerning and to keep an eye on.