Secondary action

Brewed a ipa three weeks ago. Racked into a sanitized better bottle three two days ago in order to dry hop. Added two ounces of pellets in a paint strainer with two stainless bolts as weights. Checked this evening and the beer is moving almost flowing and coming up into the airlock. The beer coming into the airlock does contain some hop particles/sludge. I did fill the bb almost all the way to the top. Wondering what is causing this movement? Any ideas?

probably what's called "offgassing" due to adding hops. just getting rid of extra co2. if the hydrometer says it's stable a couple or 3 days in a row, bottle/keg

Agree with last poster. Beer absorbs a certain amount of co2 during fermentation, dependent on temperature.