The example says:
s1 "aabcc"
s2 "dbbca"
s3 "aadbbcbcac" is interleave,
if we decompose: s3
"aa" "db" "bc" "bc" "a" "c"
s1 s2 s1 s2 s2 s1
It is not interleaving right?
Definition of interleave on test examples

You are somewhat correct, in that the decomposition you gave is not interleaving.
On the other hand, the patterns1 = aabcc s2 = dbbca
does work.
aadbbcbcac aa dbbc bc a c s1  s2  s1 s2 s1
Interleaving does not mean that the segments must be the same length, only that by advancing in one string at a time, we can recreate s3.