Glossy probably means an "over produced" sound. Instruments with no imperfections. He likes sampling instruments that have lots of noise and imperfections - and he demonstrates it's easy (for him) to bring in samples and generate custom instruments.
This generation is actually less "glossy" than the past. The electric piano, for example, has more "dirt" than previous generations. Which is a good thing. This is going in the right direction. The new rotary speaker effect (usually paired with organs) has more "dirt" than the first rotary speaker effect.
I think the general notion that perfection is sterile is something Yamaha has been taking to heart and trying to combat in the latest content and effects. Also, Genos does have some interesting features such as drum wave cycling which helps in this arena. Not sure what of this may make it to a synth in the future.
I like that he admitted the modx was too glossy for him. maybe its the sounds hes referring to. "Very glossy stuff"
He likes analog. I cant put my finger on it but I know what he means.
Watch Cukoos other videos to see what synths he normally plays on and how he programs them. I would love to see the followup to see what he thinks of programming these
There was a hint of a possible follow up video which would dig into the sample loading and programming. Although I have a fairly good inference of what was done (i.e. guess), I think MODX users would be interested in how to easily load and create their own custom sample content without the use of helpers like samplerobot.
I think Cukoos approach would be enlightening and entertaining.