Did quark matter strike Earth?

From the BBC, Did quark matter strike Earth?

A group of researchers have identified two seismic events that they think provide the first evidence of a previously undetected form of matter passing through the Earth. The so-called strange quark matter is so dense that a piece the size of a human cell would weigh a tonne….Other scientists are tantalised, saying that while these seismic disturbances are unlikely to have been caused by strange quark matter, they do not as yet have alternative explanations….