That's a different meaning of endosymbiosis at a more macro scale. This is cellular endosymbiosis. Having bacteria in your gut is not the same as having them be integrated at a molecular level into your cells as an organelle. You're scepticism of the media hype claim is correct though, there are other well known examples of endosymbiosis like this occurring, primary and secondary. Perhaps not primary with cyanobacteria but thats hardly some huge "scientific leap" in understanding or astonishment compared to some of the other stuff we know about.

Ironically you do see this kind of cellular endosymbiosis amongst the endosymbionts within insect guts with the most extreme example probably being Mixotricha paradoxa https://en.wikipedia.org/wiki/Mixotricha_paradoxa

Hatena arenicola https://en.wikipedia.org/wiki/Hatena_arenicola is very similar to this new finding, but with an algae instead of a cyanobacteria so its a secondary endosymbiosis which if anything is actually more interesting and bizarre.

We also know from the genome of Smybiodinium that its undergone quite a few endosymbiotic capture events some secondary with algae but quite likely some primary with bacteria too https://en.wikipedia.org/wiki/Symbiodinium