Ok. Did you let him get settled in and get a few meals in him?
It is recommended that you let your new snake get settled in for at least a week prior do doing much handling. Handling prior to allowing the snake to get settled can lead to stress. Over handling can also lead to stress. Stress can lead to feeding refusals and since your boy was underfed prior to coming to you, feeding should definitely be priority number one.
I personally like to wait until my new snakes have had 3 consecutive meals prior to doing much handling.
I only ask because you shared a few pics and talked about him being out for your yoga sessions. I just don't want you to end up with a stressed snake who turns into a finicky eater. BPs are tricky enough with feeding as is. Adding stress may just make things worse. Just trying to save you some potential headaches. You've got 30 years to hang out with your pet, so letting him get settled in and eating now is important.