Chances of radiator crack just after H2O pump, thermostat & rad. hoses replaced?

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After an instant overheat & engine shut down my 2003 Nissan Xterra (137K miles) was diagnosed as having blown H2O pump & thermostat that were replaced along with tensioner, belts, radiator hoses & fluids. 4 days later it overheated again on highway (smoking this time) & same service center said that coincidentally the radiator developed a crack around the neck causing it to leak coolant causing overheat. I feel like this issue is directly related to the problem/work from the previous weekend but they say it is not & that their previous tests showed no radiator problem & it's cracking was just coincidental in timing to previous overheat. I'm suspect that these 2 very related problems in same area are separate & unrelated issues & was looking for advise from someone more technical regarding your thoughts on these being coincidentally unrelated issues? Thanks in advance for your advice!