Yes, the SEC is interfering in other country's sovereignty.
I don't understand why Telegram didn't mount a 1st Amendment challenge to the SEC's authority (a blockchain is a digital printing press).
Also the SEC's interpretation of Howie is dubious - should have been appealed right up to Supreme Court.
Perhaps they didn't want to continue with the expensive fight?
That's the only thing I can think of: the sheer unproductive nature of this litigation for Telegram. It really doesn't fulfil any business need for them.