In reality, Tensor G1/G2 chips are custom-designed by Google and built on a different block and node, though they do share some parts like CPU design and DDR controller and blocks with Exynos chips.
The CORE design of the Tensor G1/G2 chips is based on the Exynos 9820 found in Galaxy S10. Google replaced the Mongoose cores with Cortex X1 cores, added the Tensor Processing Unit, and Titan Processing Unit, made changes to the decon, mfc and swapped the memory controllers from newer Exynos chips.
Some mentions of Exynos 9820 can be found in the GS101 device tree for building Android, like the reference to sound_trigger.primary.maran9820 and A-Box Service Daemon, which is used in Exynos chips for audio.
Other SoC vendors do similar things as well; for example, Qualcomm used various parts from older chips to make the Trinket platform. The Snapdragon 665 uses parts like Alpha PLL Snapdragon 652, MDSS PLL from SD 821, OSM from SD 845, and MDP Block SD 855 but is built on a different node and has a new MDP block, making it a newer platform.
In conclusion, Google Tensor chips are custom-designed to meet Google’s specific needs and are not based on or modified versions of Samsung’s Exynos chips.