As a matter of terminology, albino guinea pig actually refers to a white fur guinea pig, whose genotype is homozygous recessive (bb).
If it crossed with a black fur guinea pig and gave 5 black fur offsprings, there is a good chance that the black fur parent is homozygous dominant (BB).
The Punnett square would be as follows:
B B
b Bb Bb
b Bb Bb
So they are all heterozygous black fur offsprings.
However, it is not impossible that the black fur parent be heterozygous, namely
B b
b Bb bb
b Bb bb
Giving a 50% chance on each colour. Thus it is possible (with probability 1/32) that all five offsprings are heterozygous black fur if one of the parents was heterozygous.
In the second case, a homozygous recessive and a homozygous dominant parent will never give a white offspring. So it is sure that the black fur parent is heterozygous, with the following Punnett square:
B b
b Bb bb
b Bb bb
With a 50% probability for each of Bb (black fur) and bb (white fur).
the distribution 4,3 demonstrates this perfectly.
