Nobody in the military or foreign service world think this was indiscriminate. So you can make up your own definition of discrimination, but this was a highly targeted attack.

Proper discrimination is a question of the feasibility of treating protected persons as distinct from soldiers. Period. This attack did that by intercepting pagers marked for Hezzbollah, rather than pagers marked for general sale to the public. See the difference? The attack treated military targets as distinct from the general public. Therefore, nobody can say the attack was indiscriminate. That's just not what the word means.

If it was discriminate, was it proportionate? The 3,000 pagers were for 3,000 members of Hezzbollah, and specifically those members whose work could not be done in cell phones because of the secret military nature of the communications and Hezzbollah's fear that the cell networks were compromised. That's a very valuable target. Killing them would be a huge strategic advantage, especially in the midst of daily rocket attacks, being coordinated on the very pagers that were turned into weapons. The chance that some Hezzbollah member doesn't use the pager given to them by their employer, and instead gives it to some innocent person is minimal. The chance that someone standing nearby the person also gets hurt was very high. I think the strategic advantage clearly outweighs the risk. Virtually all 3,000.of the pagers were going to be in the hands of the people responsible for coordinating conducting the rocket attacks against Israel which are actually discriminate.

Further, it's the incidental civilian casualties that must be avoided, not the accidental ones. In other words, that a guided bomb may have a guidance malfunction and strike a civilian target does not ex ante make the attack indiscriminate. There was clearly going to be both come incidental civilian casualties and some accidental casualties. Incidental being the case where, for example the target is struck correctly but maybe was driving when the pager detonated, causing the car to crash into civilians. That's incidental. Accidental is the pager gets picked up by a kid instead of the Hezzbollah member that owns it. It was not feasible to limit those casualties, so the strategic advantage must be balanced. See how this logic works?

Here's a good article on the legal analysis that focuses on the order, and the logical sequence of the analysis. https://www.ejiltalk.org/a-lethal-misconception-in-gaza-and-beyond-disguising-indiscriminate-attacks-as-potentially-proportionate-in-discourses-on-the-laws-of-war/

The problem with doing the analysis out of order, is that if you do, you will find that all anyone has to do to win any war ever is bring their families to the front. Suppose your country is being invaded, and all the invading soldiers have their families with them. You agree that you can kill the soldiers and their families right?

That kind of gets back to your point about people being both civilians and fighters. That's not a thing. If you're a fighter, you're a fighter. If you're supporting fighters, you are also a fighter.