I wouldn't have thought the Rest hitbox would be able to reach Pikachu in the suplexed position, but I guess lots of weird stuff happens when the cloud disappears and all of a sudden everybody resets.
But would it be a combo? I'm not sure there is any way to escape being hit, especially with Jigg's Rest invincibility. It would be a matter of Pikachu being able to get an attack out before the Rest, which is impossible, assuming the Rest was perfect.
Technically, I don't think it was a combo... but hey, it looks to be inescapable, what with Rest's speed and all.
However, if it had been another Jiggly, I suppose a Rest would have avoided the hit, and sent them both sleeping to their death.