Not at all. At 7½ months, everything your son can get into his hands is likely to be put into his mouth…or at least he’ll try to get it there. That is why companies like Fisher-Price® have to make certain that every toy is made of non-toxic materials and that parts of toys are too big to be trapped in the baby’s airway should he get it all the way into his mouth. It’s a kind of “Tinker-to-Evers-to-Chance” routine: first, the baby will pick up one piece of the stacking ring, then transfer it to the other hand (possibly shaking or banging it in the process), and then put it right in the mouth. To some extent, this is related to the process of cutting the baby teeth; those gums need stimulation. But it is also a method of learning about objects.
Incidentally, one criterion of a “good” toy is that it can be used more than one way. Take the nesting cups: they can be stacked to make a tower; or they can be put one inside the other; or one can be used to hide a toy underneath; or, a small doll can be put inside and pushed around. In time, your baby will put all the rings on the stacking toy, and in the proper sequence, but for the time being how the pieces taste may have more appeal than how they look when they’re stacked.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.