Strontium is in the same family as calcium, and thus behaves chemically similar to calcium. That means it deposits in bones and other tissues that have high calcium content.
And yes, this article is heavy on the vague fear-mongering.
Yes, this article is vague.
“...strontium-90, cesium-137, cobalt-60, and nickel-63, and isn’t limited to tritium contamination.”
The tritium could come from the primary cooling system, but the others are products of the core, which could indicate a core leak into the coolant. It could also indicate improper handling of spent fuel rods or leaks in the spent fuel storage pools. None of those are good, but are much different in the dangers they pose. A one-off spill is quite different from a core leak into the coolant.
Much more information is needed.