BMW Driver upset with me

The truck ahead was indicating to move into the next lane, so I gave some time to indicate to move into my next lane, considering that there was still another lane for the bmw to overtake me. That BMW was at least two soccer fields behind when I moved over but suddenly accelerated right behind me flashing his lights, then overtook me, then braked in front of me. When I eventually went past him he had his arm out his window trying to show me something. Not sure what.