semi with right signal indicating plan to re enter right lane where we are

by Betty
(PA)

The road was busy 3:30 p.m. We drive 65 mph. A dark blue Premier transportation semi behind us signals a lane change, gets into the left lane, pulls alongside us, and signals right to enter our lane.

Were we in his blind spot? My husband sped up to 80 to get ahead of him, so there was no accident. Was he inattentive?