okay, so.

the meter used to be how long a line had to be on a pendulum for it to have a periodicity of one second. This got re-evaluated and standardized to what it is now, which is 1/10,000,000 the length between the equator and the north pole. but that number itself was chosen because it's pretty close to what the meter was before it was set to that value. So the length of the line to get that period on a pendulum is about a meter, and gravity also has an effect on the speed a pendulum swings.

https://medium.com/@roitman.io/a-wonderful-coincidence-or-an-expected-connection-why-%CF%80%C2%B2-g-6e2f9a04e30e

I read something about it on stack exchange, but couldn't find that link anymore, but the one above has the same info