in a new tank with no fish there should be little too no nitrates.. I would not rush into adding inverts and toss in the shrimp for a few days to see what happens.
Nothing good happens fast in this hobby. Feeding a small amount of flake food IMO
is not enough to trigger a cycle so go with the shrimp. Waiting a few more days so your sure IMO
is the way to go.
Is it possible you had no cycle .. yes if the LR