I'll bet Mario Coyula knows. He is a wonderful Havana architect and urban planner I interviewed a few years ago. I am sending him an e-mail to see what he says.
Anyway, I found some biographical information about Prieto here (in Spanish). He is the same architect who designed the Hotel Vedado, which is just a few blocks east of La Rampa in Havana.
Another article mentions an Alberto Prieto apartment building. The architect lived until about the age of 90 and died in 1991.