From what I always understood about the game and reading many many manuals and guides is that technique is simply the range of skills a player can pull off in his particular skill set.
A striker with 20 finishing and low technique will still be deadly in front of goal.
A striker with 20 finishing and high tech will be just as deadly, but will be able to pull off bicycle kicks, outside of the weak foot goals, and cheeky chips. HOWEVER, if said striker has low creativity/flair he will be less likely to perform those moves. Zlatan Ibrahimovich for example
A midfielder with low technique but otherwise high midfielder stats will perform very well.
The Same midfielder with high technique can (depending on creativity, flair, concentration amongst others) pull off weighted long balls, curling long shots, chipped through balls, and with high first touch will be able to collect balls from impossible angles. Ozil IRL is a perfect example of high technique Midfielder.
A defender with low technique but high defense stats will guard your line faithfully.
A defender with high technique will be better at chesting balls down, hitting headers at weird angles, performing hooking slide tackles. But you won't find many defenders with high technique as 1. They don't need it as much and 2. There are less possible skills.
A goalkeeper with low technique (really really low) and high GK stats will be a brick wall.
A goalkeeper with relatively high technique (8-10+) would be capable of the scorpion kick (depending on flair/creativity/eccentricity) and other crazy unorthodox saves. Similar to defenders, their technique levels are lower as their isn't much use for technique or a long list of tricks to master. How often do you see Hart/Lloris/Chech pull off a crazy stunt/save? Hence their lower technique.
This IS how technique is handled in FM and has always been handled and I've seen it first hand. Why they felt the need to add it to Goalkeepers is a little lost on me, but perhaps it's an attempt to make goalkeepers seem more original (previous versions, they all played pretty **** similar regardless of eccentricity).
I hope this opens some eyes or helps some of you in the game!