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.
Sure, it seems to be this Regent that wants to make "seaglider" a thing.
You can understand why they don't use "ekranoplan" as the marketing term. Its going to only be familiar to those who are into Soviet History, Aviation trivia or specific Sci-Fi.
And it's not going to bring small, modern, electric craft to mind.
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.
"Our vehicle, called a seaglider, is an all-electric, wing-in-ground-effect craft that operates within a wingspan of the water's surface and couples the speed of an airplane with the operating cost of a boat."
