Strength doesn't matter here as much as melting point. When they say tougher than Iron, I imagine they mean it ablated less in the atmosphere. I don't know what elements that might mean. Certainly not platinum group metals. Tungsten possibly. Carbon or diamond. Or alien tech.

Edit: "Based on the speed of the meteor and how much of the object burned upon entry, Loeb determined that it must be made of a material that is tougher than iron."

Yup.

As your quote says, titanium has a higher strength to weight ratio. It's not necessarily stronger, and it's not necessarily "tougher" against the circumstances described than whatever type of iron they think it might be. The meteor isn't out to minimize weight. The strength to weight ratio isn't relavent here at all and does not make titanium more likely to survive until the object comes to rest on Earth.