Bro, this statement is not true.
Copper has much higher heat transfer coefficient compared to Titanium.
In other words, copper is a much better heat conductor than Titanium, hence a better candidate for use as heat exchanger materials. One reason why Titanium is used is the corrosive nature of our salt water; the need to use additional material to isolate copper from contacting with tank water, which some how compromise its heat conductivity a little (depends on material use), etc. (I am not expert in this area though )
My 2 cents.