If this were true, the experiment would have lasted 1 generation, eh? Some had resistance or else they would not have survived to produce offspring. Duh.
One bacteria without resistance is put in an algae dish.
That one bacteria reproduces into a colony of lots of bacteria.
Some of those bacteria have resistance. When the anti-biotic is applied the resistant bacteria will survive.
Where did resistance come from if the original bacteria was non-resistant? Mutation