Use of Creative Commons as emoji on Mastodon instance

Couple of weeks ago mastodon instance “Mastodon.ART” added icons from Creative Commons project to the arsenal of custom emojis to be used in toots (posts). One user wondered if this use is legally correct, so after some discussion I sent an email to Creative Commons about it and after a week or so got an answer. I’m replicating this correspondence here to put their answer in perspective.

I attached a screenshot of custom emojis on mastodon.art:

Their answer was: