No Lemons are not the same thing as Calamansi.
Calamansi fruit is actually a Philippine lime and also known as calamondin.
The calamansi fruit is an economically important citrus hybrid predominantly cultivated in the Philippines.
It is native to the Philippines and surrounding areas in southern China, Taiwan, Borneo, and Sulawesi. Calamansi is ubiquitous in traditional Filipino cuisine.
The lemon which is a Citrus limon Osbeck, is a species of small evergreen tree in the flowering plant family Rutaceae, native to South Asia, primarily North eastern India.
So Lemon and calamansi are similar and have a similar taste and health benefits are good from both of them but they are different.