Yes, absolutely. Even one copy-pasted sentence among 50 other sentences is considered plagiarism if it was stolen from someone else without providing the source where it came from.

It is, of course, possible to unintentionally write the exact same sentence like someone else did somewhere, especially if you are explaining certain crypto terms. Or if someone asks you who is Satoshi, it's very probable that strings such as 'the anonymous bitcoin creator' would be mentioned hundreds of times. There are few ways to explain it differently.

But in this case, there is no doubt that the post was plagiarized from Reddit or somewhere else he saw it.
The admins agree because he has already been banned.