We only have the words of WotC to go by, but since their main motivation is to lure in new spending players so Ca$hbro gets more money, I don't see why they would lie on this specific topic. By their own admission, "Low complexity" was tried for years to attract new players, but that actually failed and didn't appeal to new players at all. Excitement and dynamic gameplay is what they want, not simplicity. They reiterated that point by saying that data suggests that complex cards with cool and unique mechanics actually draw new players in, as they find them cool and want to learn more, and that commander is succeeding with new, casual players partially because of that. So, to answer your specific questions.
Are we sure they like cards with a lot of words? Or do they like complex cards?
New players like complexity on cool cards, and they don't like low complexity. It's not the number of words that matters per se, but apparently they are not turned off by a high word count.
Or do they specifically like Gollum?
It's not specifically Gollum they like, it's just the card they liked the most. I don't know if other examples were named, but WotC did state cool complex cards in general are drawing in new players, whereas simple cards don't. Even a newbie recognizes when cards are boring, it seems. We can (and do) complain about increased complexity and word count on this forum, but let's be honest, when did you last see someone get excited over
Thraben Purebloods?
And are we sure it’s not only newbie players who like it and actually all of people?
I assume WotC is honest in this regard as well. By their own words they are talking about newer players here, not about heavily enfranchised older players.