The contribution and the stack traces are related. The stack traces are the number of times that Dynatrace has seen that method call pattern within the timeframe you selected. The contribution is showing the number of times each method was called within the stack traces. So the stack trace count is a sum of all the contributing method calls.
In the screenshot below you can see that the total stack trace samples is 5.8K and if you were to hover of the contribution and sum the parts it would be 5.8k as well. Similarly, the JMSIntroscope method had a stack trace sample of one and the contrubution bar seems empty compared to the other methods (since the count was so low) and it matches the stack trace with a value of one.