There isn't any particular trait in a mod that defines whether or not it's a magic mod, or a tech mod. It's not a precise thing, it's more of a feel.
Does smelting redstone and putting it in a conduit, making a block that pulverizes ores into dusts, or making engines to produce energy feel magical? Not really. Does putting items in a cauldron to smelt them down into "basic aspects", using your own blood for power, or generating energy from flowers feel magic? More so than the others. A lot of it is about the names of objects and how they look. Take Botania for example. If you change the flowers to machines, change the spreaders into lasers, and change the mana pools into energy cells, boom, it's now a tech mod. Obviously, it works vise-versa as well.
The question is, what gives off that magical or technical feel? It's about the names of things. Most tech mods have an energy system. It's clear, concise, straightforward, and usually doesn't vary between mods. Magic mods are more fickle. There really isn't a set type of energy production or consumption mod to mod. They're all rather different. It's the nature of the power generation as well. Blood magic uses well, blood. That's not something you'd expect, particularly in the real world. Tech mods use things you would expect, steam, lava, coal, etc. Very normal, very much something you'd use in real life.