A coincidence is something that seems related but isn't: https://www.merriam-webster.com/dictionary/coincidence However, "no small coincidence" implies that it's very unlikely that two (or more) things occured independently of each other. - It's no small coincidence that the company that won the contract is owned by the brother of company that tendered it. - It's no small coincidence that the river became polluted after they built a factory next to it. It's not always bad: - It's no small coincidence that they located their five star hotel on this beautiful tropical island. - it's no small coincidence that the research centre is located on the coast of Australia. Where they have a diverse habitat and extensive reefs.

Same meaning as "it is definitely planned", "it is not a small coincidence". A coincidence is when something unusual happens with no connection. For example, Stephen Hawking died on Einstein's birthday and the day of Galileo's death. = perhaps a coincidence An example I found on the web. "It is no small coincidence that CTDC, the leading dolphin assisted therapy center in the world, is located on the beautiful tropical island of Curaçao." = not an accident / it was definitely planned