ghosty, I agree with you that a 2 hour rest in the afternoon seems worrying. Fine if it's seen as a quiet time with lights turned low and some toys in the cot to play with, as bloss describes. Also fine if the little boy takes a siesta because bedtime is very late in the evening, as GRMUM describes, but if it's neither of these things then yes, I'd be curious and worried.
That's the only thing about your friend that sends alarm bells ringing for me BTW.
FWIW I think you can and should chat to your friend about this nap routine and I think you can do this without offending her if you are careful. And you strike me as a sensitive person and someone who would not offend.
Going on my own experience, amongst my friends talking about sleep patterns and problems is not really taboo anyway - so many parents suffer because a baby or child doesn't sleep to the book. An unusual sleep patten - or rest pattern - is not really something that can be construed as bad parenting IMO. And to me a 2 hour rest period in a darkened room, when the child doesn't sleep, every day, is a bit unusual. So I think you are quite within limits to openly express surprise at this routine and ask more about it. It doesn't have to come across as a criticism of the mother.
If you can do this, it might give you more reason to worry, or it might make your friend more aware of the unusualness of her routine, but hopefully it will put your mind at rest.