I have to say it is extremely unlikely you got Steam just for the discount and didn't already have steam. The construct 2 sale isn't really advertised anywhere and is instead one of their generic holiday sales.
I assume you already had a steam account and knew how it worked then were upset when you thought it would be different for Construct.
Any rate Steam isn't bad, I use the steam version no problem, did have it crash once but that was it. Construct does have a really nice feature called "save" which makes a copy of your work for you so crashes are not a big dilemma.
Also Valve has said numerous times they would allow users to back up their content in the event that they go bankrupt, which will not happen for a long time.
So just relax, the problem has to be on your side,check all your drivers not just video card, adjust your firewall, try offline mode in steam, try the free version from this site see if you have same issues.
He said he didn't have steam account, then he didn't. Who are you to say otherwise? And throw a bunch of spices into the mix with your assumptions (bit of an a$$ attack on him don't you think?)
Steam advertises everywhere. And google Construct 2 discount. And word of mouth. And don't forget social - twitter has tons of steam sale and construct 2 steam sale etc and facebook has a bunch etc etc etc etc.
Also, STeam have loads of issues - I've used them for years upon years. They just have some good pro's going for them that outweigh the cons.
I have steam version - it is broken.
I have scirra version - it works like a dream.
I have both on my computer - which means steam is the culprit.
He has every right to be annoyed, frustrated. He purchased a product that isn't working. Your copy works, so you are happy. His doesn't and he is upset. Imagine yours didn't work - you would be annoyed too.
Steam breaks a dozen laws concerning their refund policy - If they trade in your country they have to abide by those laws. Paypal dispute will be easiest for refund, 45 days, and steam have to comply, but you can also have a lawyer educate them about your country laws in regards to refunds. They are quick to issue a refund when educated.
E.g 7 day cool off period etc etc etc