Isn't normal game mmr loosely dependent on your Ranked MMR? Also Gold 3 in norms at that elo isn't that uncommon either. On my silver accounts I would regularly get matched against golds and plats. Another thing that may effect it is them premading, but I'm not sure by how much because I'm pretty sure they take other things into account like MMR, # in the premade, MMR of the person filling. I just looked and he wasn't even the reason they won lol. He was tied for second least amount of gold beaten out by his unranked and silver team mates, and he barely had second for most farm on his team still being beaten out by a silver. You probably got camped by the Rek'sai who was silver 3 last season and popped off.
I always tell my friends not to worry about the rank of the enemy team. Just play like you are equals. If you aren't worrying about being outplayed I feel it makes it less likely that you will be because you aren't playing on uneven footing or at least an uneven mindset. Whether you believe rank denotes skill, a rather dramatic difference between his elo and yours, is debatable. I don't think there is that big of a difference between gold 4 and silver 4. I mean sure the players are a bit more knowledgeable, but it's honestly the same shit. I don't think playing with higher elo people is a bad thing. It should help you improve as a player and can maybe give you an idea of if you deserve your rank or if you should be higher, I mean that in the loosest way possible. It's about learning how to carry those games and not blame your team being lower rank or bronze.
All in all everyone has those games. Probably even that gold 4, but that doesn't mean that it's a bad thing or that the match making system is broken. I feel it helps us grow as players.