That's not true. Preventing jams can actually require more complicated designs. To avoid jams the device should limit the range of motion a device is capable of and deal with dirt and debris. That can require additional parts to stabilize the motion, sealed components, specialized alloys to match thermal expansion, or more complicated motions that clear contaminants.
Given equal precision and alloys used in construction a musket will jam less than a more complex gun. However a musket and bullets built with 1700 technology/precision will jam more than a gun built to the best best modern standards standards (though there are some pretty bad modern guns out there too that may not stack up so well).
A bolt action is simple compared to any semi-automatic gun. Particularly if it is a single shot bolt action thus dispensing with the complexity of a magazine feed.
I think this is a bad analogy made with good intentions. Guns jam because the physical nature of the material is simply degradation. You need to actively fight against it by producing higher precision guns, use more advanced / tougher materials and come up with mechanisms that would reduce the possibility. That's far from simple.
I fully agree with this. There is a reason long range sharp shooters use simple bolt action guns, while the vast majority of an army uses much more complex guns. A simple bolt action also happens to be the most precise gun we can make (a single shot musket would be simpler, but it wouldn't be more accurate and loading it would be a pain). You choose the best tool for the job. Properly cared for modern guns don't jam very often, and improperly cared for guns jam too often no matter how simple they are.