But I don't think we are on the same wave length.
You quote a 'Filipino who lives elsewhere' but if that person had a passport (nationality) for that country surely they would expect to be treated as a person who has that nationality, not as a Filipino, unless they choose to use that ID.
My Filipino wife is applying for Spanish Nationality. When it is granted she will be Spanish (as well as Filipino) and entitled to be treated as Spanish. She will not need a visa to visit UK or Gibraltar for example, unless she wanted to enter as a Filipino. If she visits any other country using her Spanish passport she will be treated as Spanish. That would include RF. If she entered on her Spanish Passport she would be subject to the rules applying to Foreigners.
In your second paragraph you refer to a dual nationality person. You say one was British the other held a UK passport. I do not think that the dual nationality person was obliged to behave as if they were not a Filipino unless that was the ID they were choosing to use. Had they said they were Filipino, as you say they were (British as well) I would be surprised if they could not proceed as a Filipino.
If every one who had dual nationality had to comply with the rules appertaining to both countries what would be the point of holding the second nationality?