So, to explain why I considered it a threat, first the actual definition of the word:

a statement of an intention to inflict pain, injury, damage, or other hostile action on someone in retribution for something done or not done.

Now your question:

Maybe I could bring the argument onto twitter and bring up the whole drama there ? If you ignore me I will do that

So:

• "If you ignore me I will do that"
• The first sentence doesn't really sound like you want to instigate a friendly discussion, rather move this whole ordeal into a more open space to escalate it

It's hard to read feelings or proper intentions in text, especially if someone's not native in the target language, but here the wording definitely makes it threat-alike and I hope you understand that.