here's Arestovich saying it https://www.reddit.com/r/UkraineRussiaReport/comments/1975okx/ua_pov_arestovich_in_english_says_he_and_the_rest/

here's another member of negotiating team confirming this https://www.pravda.com.ua/eng/news/2023/11/24/7430282/

Why did Russia not explain this at the start of the war? They claimed they had no plans to invade Ukraine at all and it was all a Western lie. Why?

They did explain this many times and very clearly. Why did the west not listen is the actual question.

Do you believe that “pogroms” or similar against ethnic Russians in east Ukraine were the motivation for the invasion? To what extent do you think that they were going on?

Absolutely, and it was going on to an extent that even CNN reported on this back in 2014, here's a clip you can watch https://twitter.com/paulius60/status/1611148483859255296

There's also an hour long documentary from France on this https://www.youtube.com/watch?v=bN68OfFKaWs