Hello
Using a thread? for cleaning?
Before this thread used,was there any problem in the gums already?
Salty taste means you already had gum infection and thread only injured it.
Swelling is visible only because gums are irritated.
Next Steps
Visit a dentist,this ll be inflammation of gums which is treated with scaling and a few topical agents to be applied in the gums for 5-7 days.
nothing to worry about.
Health Tips
Please share pictures of that gum area.
Better would be to visit a dental clinic as soon as possible