High tech and low tech are really outdated words at this point. It was pretty dated when I got into the hobby awhile ago. It used to actually mean a tank was using a higher level of technology. In freshwater, we have basically hit the point were any new technology isn't really getting us further in what we can do, it's just replacing older technology by being more efficient. For the most part, it tended to describe lighting and CO2, but also other equipment as well. Now, you don't need the newest technology to have high light output, LED's are more efficient and can put out more light that T5HO's per wattage but T5HO's can give you more light than you may ever need.
That's kind of were medium tech disappeared. Most tanks that we call "low tech" would be "medium tech" not more than a few years ago. A low tech tank would likely have an internal filter, T8 lighting, and no fertilizer.
Ironically, some tanks on the board really are pushing the technology factor up, more than a few tanks on the board are almost 100% computer controlled. The difference between now, and maybe 15 years ago, whenever the terms really meant more than they do now, the new technology just saves time and energy, it doesn't do anything better, outside of some fail safe stuff, it just makes everything easier, or more efficient, or both.
For me, it's really just a distinction if you add CO2 or not. My "low tech" has LED lighting and a canister filter. My "high tech" has arguably dated lighting, a dated filter design that doesn't even self prime, lacks a heater, etc. So, in some ways, my "low tech" is likely higher tech than my "high tech". It's kind of ambiguous now in how we use it, I do wish we reevaluated the terminology.