Meaning of no more likely
A different way of phrasing "A is no more likely than B" would be "A is equally or less likely to occur than B".
The above is a logical inversion, and language isn't always as logical as we'd like it to be. From personal experience, people seem to mostly intend to say that A and B are equally likely to happen.
Either of your options is right. A is technically the most correct translation, while B will mostly be what people mean by it.