Most of the time Zoophilia automatically grants a "Very bad" severity, though in this case, evidence (even if confirmed by the person themselves) is quite surface level. Severity is up to change based on new information.
In this tweet, Cronchyshark admits to having a collection of Zoophilic content. While originally only rumors, the previously mentioned tweet proves the existence of the message. It is up to the reader's discretion to evaluate the meaning, but we believe they are not joking.
Quoting this tweet:
if you take this screenshot at face value i completely understand if you think lowly of me for this. but i need to make perfectly clear this that was a completely mutual thing at the time and that the person in question was saying things of the same kind.
Being mutual changes nothing; two negatives do not make a positive here. The intent with the drops is quite obvious, and later tweets under the original one prove that they are not trying to defend it as a joke.
Quoting this tweet:
i know that saying and even thinking these kinds of things is bad in of itself. i fully understand that. everyone who knows me well knows that i am a bit of a cumbrain and i can't turn it off well. but i am not the kind of person i am being accused of. i will improve on myself.
They know it is bad, yet still act on it. Admitting something is bad does not help, in our opinion, it only increases your guilt. Being honest with yourself is the first step to improvement, and hope they take the path to better instead of using their "honesty" as a coping mechanism.