This is not an uncommon practice to stimulate a dog to go poo for show people, but doesn't squeeze blocked anal glands. Dog show people will often do the match trick before entering the ring to make sure their dog doesn't poo in the ring, which would be a DQ. Just the sulphur tip goes in and as far as I've heard, it is unharmful and not painful. I don't know too much about it because I've never used this method. I have un-blocked my dogs' anal glands, but that match stick would be ineffective for that. You have to actually manipulate the glands themselves with a gloved finger for them to drain.
Anyhow...I don't find this to be cruel and am a little confused as to why you think it's cruel. Squeezing the anal glands is probably a lot less fun for the dog.
And so is clipping the nails for some dogs, taking baths, getting their ears cleaned. If it's done correctly and gently, it shouldn't be a painful or particularly unpleasant thing, as long as the dog isn't nervous about being handled or having physical or medical type procedures done.
I found this from another source:
How To Match Your Dog To Make It Poop
How To Match Your Dog To Make It Poop
Take one or two paper matches and put the sulfur tips briefly in your mouth to wet them.
Straddle your dog facing its butt.
Pull the tail out of the way and insert the now wet sulfur tips of the matches in your dog’s anus. Deep enough that just the ends of the matches are visible and hang out just a tiny bit.
Release the dog.
Usually the dog will start squatting almost immediately to expel the matches. If the dog doesn’t, then you can repeat the steps above.
Do not insert more than 4 matches at a time. Rarely do you need to use 4 matches but some dogs are more stubborn than others.
When the dog squats to expel the matches, it will usually poop too. Don’t forget to clean up after your dog.