Yes. Interesting revelation indeed. I would like to know if this is true. I think it would be a big deal if it came to the point where it could be confirmed that Maiden had another bass player playing with them.
A literal answer to your question would be that what he tells us is not up to my specific expectations, but to him. We dont know for sure if 'the guy stood onstage and played bass instead of Steve', as you put it. So thats a good start for an interview. Lets say he did. If I could ask him anything and on a good day have it answered I would like to know what shows he played, if he had any rehearsal with the band, what songs he played, what type of bass he played.
I'm not saying I know the language best. To be honest my language used on this forum is at times barely sufficient. But I did take a few courses in pragmatics a few years back, so in regard to your [somewhat sloppy] use of the word value: value is an example of something 'belonging to the thinking subject rather than to the object of thought'. Or in other words, value is often regarded as subjective. In the case of an interview value depends on the reader's interest. I care for Maiden history so it has value to me in that sense, and for like minded people. If you Perun love pink horses an interview with a horse trainer specialized in training pink horses would be of value to you. I dont care about pink horses so an interview with a horse trainer specialized in training pink horses would not be of much value to me!