Load sensing pressure regulating valves are tough . I can't think of any way a pad Change could cause one to leak.
They can leak just through age though.
Another cause of problems is if brake fluid is very old and has absorbed a lot of water. The water in the brake fluid causes the seals to swell. Changing the fluid for new then causes the seals to shrink , leak may ensue.
My thought is problem is coincidental to time of pad Change. These things do happen.
Get it fixed and enjoy your car.
Good luck.