Things that are coincidental maybe are no more than that. However, there can be lots of reasons why hens quit laying, some harmless, others you may need to be concerned about.
If your rooster is new to these hens and they aren't used to his attentions, that can cause stress and that can affect laying.
If your roo is really large and heavy, and if the bantam hens are very small, he could exert enough pressure on them to injure internal organs. Even if he's not injuring them, mating may be uncomfortable enough to cause them to stop laying. It's generally a good idea to limit a rooster to hens that are large enough to support his weight.