Bandwidth vs sample rate in SDR

They are related, but not directly. The sample rate must be at least 2× the bandwidth in order to satisfy the Niquist criterion with respect to aliasing. However, since "real world" filters are not ideal brick-wall filters, you need to allow a higher margin on the sample rate — or accept a lower usable bandwidth.

Some texts might use "sample rate" as the definition of the individual sample rate of two separate sampling channels (often called I and Q), which could lead you to believe they're equivalent. But the combined sample rate of the two channels together is what makes the system meet the Nyquist criterion.