"seaglider" is apparently a new word for ekranoplan. The difference is, the new ones tend not to be so enormous [1].
See e.g. https://www.regentcraft.com/seagliders/viceroy and https://www.hawaiiseaglider.org/what-is-a-seaglider
It's the same craft with a different paint job
Yes, they are Wing-in-Ground craft
Thank you for bringing this up. All the marketing (and the "journalism" regurgitating it) are writing as though 'seaglider' is a word I ought to be familiar with, but have never encountered before. I had a lot of "these things seem a lot like an ekranoplane variant, but they're not calling them that" puzzlement.
One more litetal translation of "ekranoplan" is "screen glider", so sea glider isn't that far away from it.
I suspect that in this case "seaglider" is just REGENT's marketing name, rather than a term with broader uptake. All the places I'm seeing the name 'seaglider' used in this context look like REGENT's prospective customers.
The term is also being used for some underwater drones (see https://apl.uw.edu/project/project.php?id=seaglider and https://en.wikipedia.org/wiki/Seaglider).