Hi Cindy!
Well now I have a litle time. It is just a coincidence that you where asked for this info in Porto and not on other cities, it could have been the other way around. Most hosts prefer to collect this information shortly after you booked, along with check-in time and other details, but your documentation must also be verified at check-in. Those who do not ask (previously or at the check-in) are not abiding to the law.
Since 2015 Portugal has more strictly enforced a long-standing law requiring anyone providing paid holiday accommodation to record the entry, exit, and identification details of all non-Portuguese nationals who use that accommodation. This law has been brought into force in Portugal and most other EU countries at some point since the gradual implementation of the 1990 Schengen Agreement that aims to stop human trafficking and other illegal practices. In this case, it is specifically Article 45 of the Schengen Agreement and the recent Alojamento Local law in Portugal that has brought this rule into sharper focus.
The governing body that monitors the movement of foreigners is SEF (Serviço de Estrangeiros e Fronteiras or the Immigration and Borders Service).
Of course you could reply you will give the information when you arrive.