What you are doing is the brute force method of reviving a cell. Not the most gentle way by far and not recommended if you ask me.
Your observations are correct though, this is how charging cells works. The cell voltage will go up more or less in line with the amount of current you put through it. And by connecting another 18650 in parallel this is a lot of current. The voltage will rise especially fast in the voltage range where the cell has very little capacity, that is under ~2.5V.
After the current flow stopped the voltage will drop to what is known as the resting voltage or idle voltage, which is the voltage the cell has without being affected by a charging (or discharging) current. This has nothing to do with that cell being bad, it is just how cells work.
What you should be doing instead (or what I consider to be the correct approach) is selecting the cells for reviving first. I don't bother with cells below 1.5V but everyone has their own threshold. Then you need your CC/CV power supply, like a lab power supply, or a DC/DC converter module with CC/CV function. For accuracy reasons I use a proper lab power supply.
Set it to 4.2V (or any voltage above the cell voltage actually, I'm not charging the cell all the way anyway) and limit the current to a small value, just as daromer said. If the cell is between 1.5V and 2.0V I start with 50mA. The cell voltage will rise and above 2.0V I raise the current to 100mA. I continue charging to about 3.0V, further raising the current (200/300mA) on the way if necessary (i.e. if it takes too long). At this point the cell is detected by and can be charged with a usual lithium charger. You can't use them to charge undervoltage cells right from the start because they reject them.
If it is still a good cell can be determined after the cell has been fully charged to 4.2V using your preferred device. With a maximum charging current of 1A the cell shouldn't get warm during the charge. If it does then it is a bad cell. You the discharge the cell and check the capacity. Then you charge it again and leave it for a while to check back later and find out if it has lost much of its 4.2V.
There is a way to check whether the cell is bad or not during the actual "reviving process" without having to charge and discharge the cell completely. If the cell voltage still skyrockets in the region of 3.0V although there is only a very small current flowing then it probably has very low capacity. However, this isn't completely accurate and you need a feeling for what it a fast rise in voltage and what isn't.