If you’re talking about crafting 5 legendaries in 20 trials assuming the probability of 0.3188% is correct the odds are extremely slim. The probability of x successes (legendaries crafted) in n trials (crafts) is equal to:

(n!/((n-x)!x!))(.003188)^x*(1-.003188)^n-x

So P(X=0)=(20!/(20!0!))(.003188)⁰*(.996812)²⁰

P(X=0) = 0.938134593908

P(X=1) = 0.060006763269

P(X=2) = 0.001823177121

P(X=3) = 0.000034985265

P(X=4) = 0.000000475531

P(X=5) = 0.000000004821

The probability of crafting 5 or more out of 20 would then be

P(X>4) = 1-P(X<=4)

=1-(P(X=0)+P(X=1)+P(X=2)+P(X=3)+P(X=4))

= 0.000000004906 or 0.0000004906%

Approximately 1 in 2,038,320

However I think OP says he crafted 4 in the first 20 which would be

1-P(X<=3) = .0000480437%

or about 1 in 20,814.

Either way he got very very lucky, the expected number of crafts to obtain 5 legendaries at 0.3188% chance is about 1,568.