i play 4-5-1
normal backline
dmc
mr/ml
amc/amc
st

he normally plays 4-1-3-2 with dmc mc mc mc in the middle (legal)
but he appears to be countering with
dc dc dc
dmc
mc mc mc
amc
st st

that is an illegal formation right? i just found out about illegal formations so im not really sure

so my (long) question is:
is he dumb?
does he maybe not know about illegal formations?
or can illegal formations actually work?