Hmmm, that is odd to me. Poor little fella. I mean odd in the sense that - this shouldn't irritate him, if done properly. I don't get my guys expressed at all, ever. One, bc really - it should happen naturally with properly formed poos; and two, I don't think all groomers truly know how to do it properly (and, I don't bring my guys to the groomers anymore). If not done properly, they can actually injure the sac.
If you have it on hand - you could put some hydrocortisone cream, diaper cream, or even antibiotic cream on the area to help w/ any inflammation and for soothing. You could even put a bit of aloe on the area. I do hope he feels better, how awful that must feel down there, ouch! You'll get him better though in no time!
