IIRC I have seen a story told a few times on toku forums (so take it with a massive pinch of salt) that says a member of the creative team behind Agito (the producer?) was asked about it and said that for the most part the people working on the show felt that they were making something with an original story rather than a sequel, but that the reference was thrown in because they knew some of the fans would expect them to be linked (after all, the Showa Riders are all in continuity) and also because it provided them with a nice "the police have encountered something similar before" explaination for why they had already developed a high-tech power armour unit when the monsters have only just started attacking. He apparently seemed quite content to leave it up to people's individual fanon.
There was something like that, but you're mixing up the details.
(the link seems to be offline right now, but you can find previous discussions about it)
tvarc.toei.co.jp/tv/agito/msg-0205.html
Here's an alternate link:
http://web.archive.org/web/20130825011430/http://tvarc.toei.co.jp/tv/agito/msg-0205.html
It's written by Agito's producer, Shirakura, now infamous for the spring crossover movies. Anyway, the idea is that there was a lot of demand for a Kuuga sequel, but Agito's staff out of respect for Kuuga's staff, and its story, and to not make Godai's battle to bring smiles to people meaningless blurred the ties between the two series, leaving Kuuga as a fully closed tale.
Although there are references to Kuuga's events in the beginning, that text itself references that there are also some contradictions (like dates not matching up - Agito makes a reference to a "Unidentified Lifeform Number 4"... which fought against other "Unidentified Lifeforms" two years before Agito even though Agito started airing one week after Kuuga and the in series dates of both follow the real life years they aired). According to Shirakura, the contradictions exist on purpose exactly to show that Agito isn't a sequel to Kuuga.
However, he also says that they respected Kuuga's setting, and you're free to think about Agito as a Kuuga sequel if you want to think that, and they'd even appreciate that people put it on that level.
I'd also note that the references to Kuuga's events completely disappear later, and some developments in Agito don't make sense coming after Kuuga's events at that point (like the police considering humans with special powers an impossibility).