I can't answer as to people of the past in general, but in ancient Greece and Rome we find several contradictory explanations of magnets. Here are a couple important ones.

The earliest explanation is one ascribed in antiquity (whether correctly or not is controversial) to Thales of Miletus, traditionally the first Greek philosopher. On this account (given by Aristotle in De Anima 405a19) Thales argued that the magnetic force was caused by magnets having souls:

Thales, too, to judge from what is recorded about him, seems to have held soul to be a motive force, since he said that the magnet has a soul in it because it moves the iron.

This is less silly than it might appear at first, because for the Greeks self-caused motion was the main characteristic of psyche, the principle of soul or life. This is often connected with the principle of 'hylozoism' often ascribed to Thales and the Milesian philosophers who came after him, in other words the idea that life is inherent in matter in some way. The Universe is in motion and the cause of motion is psyche. Magnets are, we might suppose, a good example.

Bear in mind that this isn't arguing for the existence of some intangible, distinct, life-force in the way we might understand the word 'psychic' in English today; the idea of life as self-caused motion was understood narrowly and technically (called later the kinetikon or motive force). And of course there are problems -- Thales is claimed to have argued that all matter is "full of gods", and for lack of evidence we simply don't know how he reconciled this with the specific statement about magnets, or if he even did.

About a century later, Empedocles of Acragas gave essentially the opposite explanation, one based on purely material factors rather than psyche: on the subsequent account of Alexander of Aphrodisias (Quaestiones 72), Empedocles argued that magnetic force was actually a direct contact between the iron and the magnet, and that the magnet extended physical tendrils, called effluences, of some kind that entered pores in the iron. Only iron was attracted because only iron had the pores of the right shape.

We can find a third explanation in what we're told about the atomist Democritus. He apparently argued that like acts upon like (in various forms again a fairly common principle in older Greek philosophy), and that magnets attracted iron because they were made of atoms of similar shapes. The iron moved towards the magnet, Democritus claimed, because the magnet's atoms were smaller, and so their motion is less significant. (This is again from Alexander of Aphrodisias, Quaest. 2.23.)

Epicurus apparently combined Empedocles' explanation and Democritian atomism, and argued that magnets radiated atoms that drew in the iron. The Roman philosopher Lucretius (De Rerum Natura 6.1022) took this explanation further, and argued that the atomic effluences of magnets scatter the surrounding air particles, and the iron is drawn into the empty space. The reason only iron was attracted was that the atoms of iron are tightly bound together, meaning the whole solid would move, whereas other objects would simply shed invisible layers of particles.

(Note that I've been hedging a lot with things "we are told" about people, and "ascribed" to people -- unfortunately other than Lucretius these thinkers' own works have generally not survived, and so there are academic controversies about how reliable the individual quotations and comments on them that we get from later authorities are.)