It would be fair to say that the standard in Liga 2 is not the strongest around. Don't get me wrong, there are some very talented players and Boyd will improve his game technically, but it's not the strongest second tier.
Attendance sizes are a bit of a misnomer in Portugal, to be honest. For instance, you'd struggle to find too many well-supported clubs outside of the "big 3" - that is Benfica, Sporting and Porto. Clubs like Braga, Académica and the Vitória Guimarães first team get reasonable crouds but outside of those you're talking the lower 4 figures. I used to spend a lot of time watching UD Leiria in the top flight (they were relegated 3yrs ago). They only used to average around 1,000-1,500 for home games. The big 3 have a massive hold over most Portuguese fans nationwide.
If Boyd can progress and have a good year in the B team then there's no reason he shouldn't be playing for the Liga NOS side next season.