As someone who was in the arena but on the opposite of the plushie throw, everyone around me was laughing and found it really funny to see the rain of black plushies just suddenly come down like that. I actually had no idea that it was going to happen and must have missed the announcement about it during one of the zamboni breaks. However, it was obvious within a few seconds that it was coordinated because they had the "How To Train Your Dragon" signs and video up playing immediately.
Also, if you do follow Ilia, you'll know that HTTYD is his favorite movie and Toothless is his spirit animal. There's a livestream that he did back around 2022 or 2023 (I want to say before he even landed the 4A and definitely before any world titles) where he said he would love to have a Toothless rain one day like Hanyu did. As a result, fans have been giving him Toothless shirts and merch for years. I'm SURE that's why he even had a HTTYD ad with NBC to begin with. He had a small little Toothless rain last year after the Worlds 2025 SP which he loved. It doesn't matter that this was fan-coordinated or USFS/NBC-coordinated. What mattered is that Ilia loved it and was completely delighted, and I was really happy for him. Also, thank goodness Ilia actually had a blinder of a skate, because it would have been very awkward had he bombed it, haha.