Mathilde has not studied the liquid enough to know for sure [what it is], but the assumptions she can make based on what she knows is thus:
Creatures of magic, like the snake was/is, are not made of regular matter. They are made of magic under the creature's control so that it forms its vessel. When such a creature is slain (dis-incorporated?), said magic would usually decay back into elemental magic. The unfortunate creature being trapped in a halfway point between 'life' and 'death' (inasmuch as the two states can be applied to demons and quasi-demonic warp entities) is why, presumably, the liquid has not decayed.
The snake is not, in the conventional sense, a demon, and it is not explicitly aligned with any of the chaos gods. Therefore the magic that it is made of is not unholy magic tainted by any (or all) of those gods. Nor is it aligned with any of the winds of magic, nor is it made up of the festered and corruptive eneriges of dhar.
This is where facts run out and speculation is required.
'High' magic, of which humans know very little, is when an extremely skilled practitioner of magic uses all eight winds of magic in unison. Normally, if someone uses multiple winds of magic, the result becomes Dhar - imagine someone trying to mix paints and it inevitably resulting in a mucky brown tone. When a sufficiently skilled wizard does it, they can combine the colours into a pure magic called Qhaysh, similarly to how we are taught 'white' light is made up of all colours combined. No known human is capable of such a feat, as it (in theory) takes centuries of careful study to achieve it.
The snake's 'blood' seems to be similar to Qhaysh, but it is not quite. When magic enters the world through the polar gates, the effect the world and/or the polar gates has on it is to separate it into the eight 'winds' of magic. This is magic that never passed the polar gates, and has never been separated.
Also, magic is naturally similar to energy, or gas - it blows freely and gathers and pools according to its nature. Some extremely skilled wizards are capable of exerting their will over magic and forcing it to crystallize into a solid known as power stones, which power the most rare and puissant of magical artifacts. Magic in liquid form is unknown to you, and as far as you know, to the Colleges in general. Potions are not magic in liquid form, but derived from magic-influenced plants, animals and minerals.
The implications of all of the above are as yet untested and unknown to you.