I didn't know Soku was such a good grip fighter. Looks like he just lost focus at the end and let Karo get in on a leg. During the match, Karo attempted drop seo nage a couple of times but didn't even get close to pulling it off.
As an aside, this tape is a good example of why Judo never caught on in the US. Grip fighting with an occasional throw attempt is just not gonna appeal to a wide audience.