How does match making work?

Hi, I have played this game enough to reach the level 20. For many years I played this game only in group queues with friends because I did not make a habit of solo queueing alone.

Tonight I actually leveled up from 19 to 20 with two of my friends who were level 100 and level 80 and I don't think are ranked this season. The one who played ranked in the past was a gold player in previous tiers.

Tonight we did some chill arams and I was again trying to relearn the various champions abilities with which I have always been unfamiliar because there are a lot of them. However, for our final game of the night after being crushed several times in a row, we noticed that the enemy players were Master and Grandmaster rank.

What is the reason that my opponents are master and grandmasters and the other ranks like Platinum and Diamond that I can't keep straight when I am level 20, and nobody else on my team is a Grandmaster? Is there a way to prevent this from happening? Thanks.

(Along with my two friends, the random guys on our team were lower than level 30, so we did not have any Grandmasters or Masters or Platinum/Diamond whatever on our team.)