Perlite is foamed glass, so that doesn't seem likely, not unless is was soaked before in a denser medium (perhaps).

Take a look at the brand of Perlite you purchased. You may be suprised to find out that companies like Miracle Grow add all kinds of stuff to their products.

Here is the Miracle Gro Perlite additives: Nitrogen .04%
Phosphate .01%
Potasium .06%

Hope that helps ...

It would make an interesting experiment.

You could try pouring a glass of pure water, possibly bottled water, which would have an EC near zero. Then mix in some fresh perlite and wait to see if there is a change in the EC within a given time.

If you try this let us know what happens. Mhargraves could be correct about an additive being the source and that would be interesting indeed.

Bilberry

Did you have plants in the solution? A rise in EC with no plants could be attributed to evaporation but that much increase would be unusual. Was it really hot?

If your plants weren't very hungry, they could've simply drank a lot of water which would raise the EC (and also indicate that you should give them less nutrients for now).

But as everyone else has said, the Perlite itself won't affect EC but some manufacturers put fertilizer in their Perlite, which messes things up.